������������������������ ��������� ���� BRITISH STANDARD Specification for 100° Countersunk head steel bolts (Unified threads), cadmium plated, for aircraft ICS 49.030.20 [UDC 621.882.215.082.3:669.14:629.13] BS 2A 173: 1962+A7:2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 This British Standard, having been approved by the Aircraft Industry Standards Committee and endorsed by the Chairman of the Engineering Divisional Council, was published under the authority of the General Council of the Institution on June 1962 © The British Standards Institution 2012 Published by BSI Standards Limited 2012 The following BSI references relate to the work on this standard: Committee reference ACE/12 Draft for comment AB (ACE) 2149 11/30254197 DC 11/30254197 DC ISBN 978 580 76863 Amendments issued since publication Amd No Date of issue Comments 4655 October 1962 4735 November 1962 5312 August 1964 6164 May 1967 2123 October 1976 5385 July 1988 Indicated by a sideline in the margin A7 July 2012 May See Foreword ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Contents Page Foreword ii Scope General requirements Material and manufacture Dimensions Screw threads Anti-corrosion treatment Identification Inspection procedure Gauging Appendix A Principles of flushness control and recommended gauging practice 10 Appendix B Table for conversion of inches to approximate millimeter equivalents Inside back cover Figure Figure 1a — Enlarged view of head Figure 1b — Detail of slots Figure — Diagram (part) showing maximum and minimum head conditions Figure Figure — Method of measurement of head protrusion 11 Figure — Protrusion gauge block 12 Table — Dimensions Table — Bearing length L, clamping length M and overall length E © The British Standards Institution 2012 i ������������������������ ��������� ���� ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 BS 2A 173:1962+A7:2012 Foreword Foreword This British Standard is published by BSI Standards Limited, under licence from This British Standards Standard is published by BSI Standards Limited, under licence from The British Institution The British Standards Institution This revision of BS A 173:1956 has been prepared to relate the standard to the This revision of BS A 173:1956 has Additionally, been preparedprovision to relatehas thebeen standard relevant requirements of BS A 100 madeto forthe the relevant requirements of BS for A 100 Additionally, provision has madefor for the use of alternative materials forged bolts, the use of BS S 96been material use of alternative materials forlimits forgedonbolts, use of BSthe S 96 material machined bolts, and for closer headthe protrusion, values now for shown machined bolts, and for closer limits on head protrusion, the values now shown being the same as those given in the American specification NAS 517 being same as those given in the American specification 517 BS 2Athe 173:1962+A7:2012 supersedes BS 2A 173:1962 (incorporating Amendments 173:1962 which NAS is withdrawn BS 2A 173:1962+A7:2012 supersedes BS 2A 173:1962 which is withdrawn Nos 1:1962, 2:1962, 3:1964,by4:Amendment 1967, 5: 1976 and 6: 1988), is withdrawn Text introduced or altered No 7(and No 3)which is indicated in the text Text introduced byamendments Amendment are No not 7(and No 3) is indicated in the text by tags and or altered Previous indicated by tags and Previous are not This British Standard marksamendments a departure from theindicated traditional method of This British Standard marks a departure from the traditional method offor head dimensioning countersunk head bolts by means of toleranced dimensions dimensioning countersunk head bolts by means of toleranced dimensions for head diameter, head thickness, land and angle The method now adopted is known as diameter, head thickness, land and angle The method now adopted is known the “flushness tolerance” method and was first used in a British Standard for as the “flushnessfasteners tolerance” was first used in a British for countersunk in method BS 1981,and “Unified machine screws and Standard machine screw countersunk fasteners in BS 1981, “Unifiedare machine screws and machine screw units.” Its basic principles and advantages outlined in Appendix A to this units.” Its together basic principles and advantages outlined in Appendix A to this standard, with suggested methodsare of gauging standard, together with suggested methods of gauging Reference is made in the standard to the following British Standards: Reference is made in the standard to the following British Standards: BS A 100, Bolts and nuts for aircraft (general clauses) BS A 100, Bolts and nuts for aircraft (general clauses) BS EN 2133 Aerospace series Cadmium plating of steels with specified tensile Aerospace series.copper BS EN 2133 Aerospace series Cadmium of steels with ≤ 1450 strength MPa, copper, alloysplating and nickel alloys specified tensile ≤ strength 1450 MPa, copper, copper alloys and nickel alloys BS S 95, 55 ton, 1" per cent nickel-chromium-molybdenum steel BS S 95, 55 ton, 1" per cent nickel-chromium-molybdenum steel BS S 102, Carbon-molybdenum steel BS S 102, Carbon-molybdenum steel BS S 105, Carbon steel BS steel BS S S 105, 114, Carbon 55 ton manganese-molybdenum steel BS S 114, 55 ton manganese-molybdenum steel BS S 116, 55 ton carbon steel BS ton carbon steel BS S S 116, 117, 55 55 ton per cent chromium steel BS S 117, 55 ton per cent chromium steel BS S 147, Nickel-chromium-molybdenum steel (bar for the manufacture of forged BS S only) 147, Nickel-chromium-molybdenum steel (bar for the manufacture of forged bolts bolts BS S only) 148, Low nickel-chromium steel (bar for the manufacture of forged bolts only) BS steel (bar for the manufacture BS S S 148, 149, Low 1.75 nickel-chromium per cent nickel-chromium-molybdenum steel of forged bolts only) BS cent nickel-chromium-molybdenum steel bars, forgings and BS S S 149, 154, 1.75 2" %per nickel-chromium-molybdenum steel billets, BS S 154, 2" % nickel-chromium-molybdenum steel billets, parts (880 – 080 MPa: limiting ruling section 150 mm) bars, forgings and parts (880 1– % 080 MPa: limiting rulingsteel section 150 BS S 158, chromium-molybdenum bars formm) the manufacture of forged BS S 158, % chromium-molybdenum steel bars for the manufacture of forged bolts and forged nuts bolts and forged Reference is also nuts made to: Reference is alsoElectro-deposition made to: Def Stan, 03-19 of cadmium Def Stan, 03-19 Electro-deposition of be cadmium NOTE The values in British units are to regarded as the standard A table is given in Appendix to provide ready means of calculating the approximate millimetre NOTE B The values ina British units are to be regarded as the standard A tableequivalents is given in of the inch dimensions More aaccurate conversions should be on the tables in BS equivalents 350 Appendix B to provide ready means of calculating thebased approximate millimetre of the inch dimensions accurate conversions shoulduse be based in force, BS 350 NOTE In placeMore of the customary, but incorrect, of the on tonthe as tables a unit of the unit called a ton force tonf) has beenbut used in this standard is as theaforce acting on aa NOTE (abbreviation In place of the customary, incorrect, use of theItton unit which, of force,when the unit called bodyforce of mass one ton, gives acceleration equal that of standard ton (abbreviation tonf)an has been used in thisto standard It is the gravity force which, when acting on a body of mass one ton, gives an acceleration equal to that of standard gravity CAUTION BS A 173 bolts have cadmium as a plating material which has been CAUTION BS Abanned 173 bolts cadmium as a plating material which has been restricted and/or forhave use in many countries owing to environmental and health restricted and/or banned owing to environmental and be health concerns; they should notfor be use usedininmany new countries product designs Local officials should concerns; not be used in new product designs Local officials should be consulted they aboutshould any concerns on the use of cadmium-plated parts consulted about any concerns on the use of cadmium-plated parts A British Standard does not purport to include all the necessary provisions of a A British Standard does purport to include provisions This publication notnot purport to include all all thethe necessary provisions of aof a contract Users ofdoes British Standards are responsible fornecessary their correct application contract Users are responsible for itsare correct application of British Standards responsible for their correct application Compliance with a British Standard does not of itself confer immunity Compliance with confer immunity from legal Compliance with a a British British Standard Standard cannot does not of itself confer immunity from legal obligations obligations from legal obligations Summary of pages Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, This comprises a front cover, inside front cover, pages i and ii, pagesdocument to 12, an inside back cover and aanback cover pages to 12, an inside back cover and a back cover This standard has been updated (see copyright date) and may have had This standardincorporated has been updated (seebe copyright date) and may have had amendments This will indicated in the amendment table on the amendments incorporated This will be indicated in the amendment table on the inside front cover inside front cover ii ii © The British Standards Institution 2012 © The British Standards Institution 2012 BS 2A 173:1962+A7:2012 BS 2A 173:1962+A7:2012 Scope Scope This British Standard specifies the materials, dimensions and inspection requirements This Britishfinish Standard specifies the materials, for steel bolts with 100° countersunk heads and Unified dimensions, finish and and inspection inspection requirements requirements for dimensions finish for threads , cadmium plated, for aircraft steel bolts with 100° countersunk heads and Unified threads , cadmium plated, for aircraft General requirements General The bolts shallrequirements comply with the relevant requirements BS 4A with 100:2003 in respect of The bolts shall comply the relevant manufacture, screw threads, and requirements BS 4A4A 100:2003 inprotective respect of of requirements of BS 100:2003 in respect finish manufacture, screw threads, and protective finish Material and manufacture Material a) The bolts and shall manufacture be manufactured by either of the following methods: a) The bolts shall be manufactured by either of Machinedmethods: from bright drawn alloy steel thei)following bars that conform to the drawn latest issue one of i) Machined from bright alloy of steel the following British Standards: bars that conform to the latest issue of one of BS Sfollowing 95 the British Standards: or BS S 114 BS S 95 116 — bolts up to and or BS S 114 including )— inch diameter; or BS S 116 bolts up to and or BS S 117 including ) inch diameter; 154 or BS S 117 NOTE S 96 material may be used until stock are or BS SBS154 exhausted NOTE BS S 96 material may be used until stock are ii) Forged from alloy steel that conforms exhausted to latestfrom issue of one of the following ii) Forged fromalloy alloy steel that conforms ii) the Forged steel that conforms British Standards: to the latest issue of one of the following BS S 102 British Standards: or BS S 105 BS S 102 or BS S 105 147 148 or BS S 147 149 or BS S 148 158 or BS S 149 b) In the Sfinally or BS 158 heat-treated condition the mechanical properties of the material b) In the finally heat-treated conditionused the for forged bolts shall be as follows: mechanical properties of the material used for 0.1 per cent proof forged bolts shall be as follows: not less than 43 tonf/in2 stress (664less MPa) 0.1 per cent proof not than 43 tonf/in2 stress Tensile strength Tensile strength Elongation on Ỉ area Elongation Izod impact on Ỉ area value Izod impact value not than 55 tonf/in2 (664less MPa) (850 MPa) not less than 55 tonf/in2 not more (850 MPa)than 65 tonf/in2 (1 MPa) not003 more than 65 tonf/in2 not003 lessMPa) than 18 per cent (1 not less than 18 per cent not less than 40 ft lbf (54 J) not less than 40 ft lbf (54 J) Dimensions Dimensions a) All finished bolts, after the application of the shall conform to theof the protective a) All finishedfinish bolts, after the application given in Table dimensions and tolerances protective finish shall conform to the1 and Table dimensions and tolerances given in Table and b) The2 clamping length of the bolt shall conform Table to and tolerances given Table 2, b) the Thedimensions clamping length of the bolt shallinconform and shall be such that, when a standard nut 2, to the dimensions and tolerances given in Table without countersink or a ring gauge without and shall be such that, when a standard nut countersink has beenorscrewed on as far as without countersink a ring gauge without possible by hand, its leading countersink has been screwedface on is as within far as the distance M hand, from the surface the bolt possible by its upper leading face isofwithin the head The runout of thread shall not exceed twice distance M from the upper surface of the bolt the pitch head The runout of thread shall not exceed twice c) The nominal length of the bolt shall be the the pitch minimum bearing length L, which is determined c) The nominal length of the bolt shall be the by the minimum less two minimum bearingclamping length L,length whichM, is determined thread pitches clamping length M, less two by the minimum thread pitches Screw threads Screw threads The bolts shall have Unified threads of the form and class of fitshall specified the relevant of The bolts have in Unified threadsrequirements of the form and BS 4A 100:2003 After coating, the bolt threads, class of fit specified in the relevant requirements of shall theAfter basic coating, size (maximum BSnot 100:2003 the boltmaterial threads, 4A exceed threads condition) for thethe thread class of fit shall not exceed basicsize sizeand (maximum material condition) for the thread size and class of fit Protective finish finished Protective finish All bolts shall be coated with cadmium alloy steel that conforms to All Forged finishedfrom bolts shall be coated with cadmium the latest issue of one of the following in accordance with Def-Stan 03-19 or Forged from alloy steel that conforms to Standards: BS British EN latest 2133. the issue of one of the following British Standards: Identification Identification The British Standard number and part number shall not be applied onnumber the bolts, butpart shall be clearly The British Standard and number marked on the labels of parcels of bolts shall not be applied on the bolts, but shall be clearly marked on the labels of parcels of bolts Inspection procedure Inspection The bolts shall beprocedure inspected in accordance with the relevant requirements of BS 4A 100:2003 100:2003. BS 4A The bolts shall be inspected in accordance with the relevant requirements of BS 4A 100:2003 Gauging Gauging a) The method of head dimensioning shown in Table definesof maximum and minimum head a) The1method head dimensioning shown in envelopes which control flushness in the manner Table defines maximum and minimum head defined in which Appendix A flushness in the manner envelopes control b) The type of gauge A shown in Figure and defined in Appendix Figure is recommended asin being suitable b) The type of gauge shown Figure andfor flushness measurement, but the type of gauge Figure is recommended as being suitable for to be used is measurement, not a mandatory of thisto flushness butrequirement the type of gauge standard shownrequirement in Figure and be used is The not agauge mandatory of this Figure does not control the angle, which standard The gauge shown inhead Figure and will require to be checked at intervals during Figure does not control the head angle, which production additional will beduring necessary will require An to be checkedgauge at intervals for the absolute minimum head diameter production An additional gauge will be necessary for the absolute minimum head diameter © The British Standards Institution 2012 © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Table — Dimensions (Third Angle Project) * For bearing length L, clamping length M and overall length E, see Table Figure Figure 1b — Details of slots Figure 1a — Enlarged view of head © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Table — Dimensions NOTE Gauges suitable for controlling flushness are described in Appendix A The limits on head protrusion not permit the extreme limits on diameter to sharp corners and on head angle shown by 1) and 2) to occur in one and the same head This is because the application of these countersunk heads demands a high degree of flushness 1) Indicates the maximum head protrusion obtainable with the minimum head angle 2) Indicates the minimum head protrusion obtainable with the maximum head angle Figure — Diagram (part) showing maximum and minimum head conditions © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Table — Dimensions Nominal thread size Decimal equivalent of nominal size No 10-2 UNF /4 in UNF 0.1640 Min length Thread Diameter of of screwed plain portion runout portion of of shank pitch shank A Fa max in in in No 8-32 UNC Ref in 0.1635 0.1605 0.063 in 0.327 10 Absolute minimum B Nominal head depthb D (For reference only) Diameter of head To sharp corners V (For reference only) max in in 0.334 0.323 in in 0.287 0.068 0.1900 0.1895 0.1865 0.063 0.377 0.387 0.375 0.337 0.080 0.2500 0.2495 0.2465 0.071 0.459 0.510 0.496 0.452 0.106 /16 in UNF 0.3125 0.3120 0.3090 0.083 0.497 0.638 0.622 0.572 0.133 /8 in UNF 0.3750 0.3745 0.3715 0.083 0.597 0.766 0.748 0.692 0.159 /16 in UNF 0.4375 0.4370 0.4335 0.100 0.670 0.894 0.874 0.812 0.186 /2 in UNF 0.5000 0.4995 0.4960 0.100 0.770 1.022 1.000 0.932 0.213 1 11 12 13 14 Head protrusion Nominal thread size Protrusion Gauging above gauging dia dia N P max in Flushness tolerance P max – P min.) in 15 16 Radius under bolt head R max 17 18 19 20 21 22 Depth J Rad U –0.010 +0 ± 0.010 Slot Depth of chamfer G max in in Width H in max in in in in in in No 8-32 UNC 0.2671 0.0276 0.0238 0.0038 0.020 0.010 0.030 0.020 0.045 0.054 in 0.045 0.219 No 10-32 UNF 0.3147 0.0299 0.0259 0.0040 0.020 0.010 0.030 0.020 0.050 0.060 0.060 0.219 /4 in UNF 0.4245 0.0353 0.0307 0.0046 0.030 0.015 0.040 0.030 0.050 0.060 0.068 0.300 /16 in UNF 0.5389 0.0409 0.0357 0.0052 0.030 0.015 0.040 0.030 0.050 0.060 0.087 0.300 /8 in UNF 0.6532 0.0466 0.0407 0.0059 0.030 0.015 0.040 0.030 0.070 0.080 0.123 0.375 /16 in UNF 0.7676 0.0522 0.0457 0.0065 0.030 0.015 0.050 0.040 0.070 0.080 0.134 0.375 /2 in UNF 0.8820 0.0578 0.0507 0.0071 0.030 0.015 0.050 0.040 0.070 0.080 0.134 0.375 a This dimension is an absolute minimum associated with maximum length M and minimum length E It is not intended that it shall be used for manufacturing or inspection purposes b These dimensions have been calculated as the mean between maximum and minimum head depth, corresponding to maximum and minimum diameters to sharp corners, the head angle and shank diameter being taken as nominal © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Table — Bearing length L, clamping length M and overall length E Figure No 8-32 UNC Part No No 10-32 UNF L M +0 –0.03 E +0.04 –0 in in in a Part No L M +0 –0.03 E +0.04 –0 in in in a 1C 2C 3C 4C 5C 0.1 0.2 0.3 0.4 0.5 0.193 0.293 0.393 0.493 0.593 0.55 0.65 0.75 0.85 0.95 1D 2D 3D 4D 5D 0.1 0.2 0.3 0.4 0.5 0.193 0.293 0.393 0.493 0.593 0.60 0.70 0.80 0.90 1.00 6C 7C 8C 9C 10C 0.6 0.7 0.8 0.9 1.0 0.693 0.793 0.893 0.993 1.093 1.05 1.15 1.25 1.35 1.45 6D 7D 8D 9D 10D 0.6 0.7 0.8 0.9 1.0 0.693 0.793 0.893 0.993 1.093 1.10 1.20 1.30 1.40 1.50 11C 12C 13C 14C 15C 1.1 1.2 1.3 1.4 1.5 1.193 1.293 1.393 1.493 1.593 1.55 1.65 1.75 1.85 1.95 11D 12D 13D 14D 15D 1.1 1.2 1.3 1.4 1.5 1.193 1.293 1.393 1.493 1.593 1.60 1.70 1.80 1.90 2.00 16C 17C 18C 19C 20C 1.6 1.7 1.8 1.9 2.0 1.693 1.793 1.893 1.993 2.093 2.05 2.15 2.25 2.35 2.45 16D 17D 18D 19D 20D 1.6 1.7 1.8 1.9 2.0 1.693 1.793 1.893 1.993 2.093 2.10 2.20 2.30 2.40 2.50 21C 22C 23C 24C 25C 2.1 2.2 2.3 2.4 2.5 2.193 2.293 2.393 2.493 2.593 2.55 2.65 2.75 2.85 2.95 21D 22D 23D 24D 25D 2.1 2.2 2.3 2.4 2.5 2.193 2.293 2.393 2.493 2.593 2.60 2.70 2.80 2.90 3.00 26C 27C 28C 2.6 2.7 2.8 2.693 2.793 2.893 3.05 3.15 3.25 26D 27D 28D 2.6 2.7 2.8 2.693 2.793 2.893 3.10 3.20 3.30 29C 30C 31C 32C 33C 2.9 3.0 3.1 3.2 3.3 2.993 3.093 3.193 3.293 3.393 3.35 3.45 3.55 3.65 3.75 29D 30D 31D 32D 33D 2.9 3.0 3.1 3.2 3.3 2.993 3.093 3.193 3.293 3.393 3.40 3.50 3.60 3.70 3.80 a See Clause c) © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Table — Bearing length L, clamping length M and overall length E No 8-32 UNC Part No No 10-32 UNF aL M +0 –0.03 E +0.04 –0 in in in Part No aL M +0 –0.03 E +0.04 –0 in in in 34C 35C 36C 37C 38C 3.4 3.5 3.6 3.7 3.8 3.493 3.593 3.693 3.793 3.893 3.85 3.95 4.05 4.15 4.25 34D 35D 36D 37D 38D 3.4 3.5 3.6 3.7 3.8 3.493 3.593 3.693 3.793 3.893 3.90 4.00 4.10 4.20 4.30 39C 40C 41C 42C 43C 3.9 4.0 4.1 4.2 4.3 3.993 4.093 4.193 4.293 4.393 4.35 4.45 4.55 4.65 4.75 39D 40D 41D 42D 43D 3.9 4.0 4.1 4.2 4.3 3.993 4.093 4.193 4.293 4.393 4.40 4.50 4.60 4.70 4.80 44C 45C 46C 47C 48C 4.4 4.5 4.6 4.7 4.8 4.493 4.593 4.693 4.793 4.893 4.85 4.95 5.05 5.15 5.25 44D 45D 46D 47D 48D 4.4 4.5 4.6 4.7 4.8 4.493 4.593 4.693 4.793 4.893 4.90 5.00 5.10 5.20 5.30 49C 50C 51C 52C 53C 4.9 5.0 5.1 5.2 5.3 4.993 5.093 5.193 5.293 5.393 5.35 5.45 5.55 5.65 5.75 49D 50D 51D 52D 53D 4.9 5.0 5.1 5.2 5.3 4.993 5.093 5.193 5.293 5.393 5.40 5.50 5.60 5.70 5.80 a See Clause c) © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Table — Bearing length L, clamping length M and overall length E /4 in UNF aL M +0 –0.03 E +0.04 –0 in in in Part No /16 in UNF /8 in UNF aL M +0 –0.03 E +0.04 –0 in in in Part No aL M +0 –0.03 E +0.04 –0 in in in Part No 2E 3E 4E 5E 0.2 0.3 0.4 0.5 0.301 0.401 0.501 0.601 0.80 0.90 1.00 1.10 2G 3G 4G 5G 0.2 0.3 0.4 0.5 0.313 0.413 0.513 0.613 0.85 0.95 1.05 1.15 2J 3J 4J 5J 0.2 0.3 0.4 0.5 0.313 0.413 0.513 0.613 0.95 1.05 1.15 1.25 6E 7E 8E 9E 10E 0.6 0.7 0.8 0.9 1.0 0.701 0.801 0.901 1.001 1.101 1.20 1.30 1.40 1.50 1.60 6G 7G 8G 9G 10G 0.6 0.7 0.8 0.9 1.0 0.713 0.813 0.913 1.013 1.113 1.25 1.35 1.45 1.55 1.65 6J 7J 8J 9J 10J 0.6 0.7 0.8 0.9 1.0 0.713 0.813 0.913 1.013 1.113 1.35 1.45 1.55 1.65 1.75 11E 12E 13E 14E 15E 1.1 1.2 1.3 1.4 1.5 1.201 1.301 1.401 1.501 1.601 1.70 1.80 1.90 2.00 2.10 11G 12G 13G 14G 15G 1.1 1.2 1.3 1.4 1.5 1.213 1.313 1.413 1.513 1.613 1.75 1.85 1.95 2.05 2.15 11J 12J 13J 14J 15J 1.1 1.2 1.3 1.4 1.5 1.213 1.313 1.413 1.513 1.613 1.85 1.95 2.05 2.15 2.25 16E 17E 18E 19E 20E 1.6 1.7 1.8 1.9 2.0 1.701 1.801 1.901 2.001 2.101 2.20 2.30 2.40 2.50 2.60 16G 17G 18G 19G 20G 1.6 1.7 1.8 1.9 2.0 1.713 1.813 1.913 2.013 2.113 2.25 2.35 2.45 2.55 2.65 16J 17J 18J 19J 20J 1.6 1.7 1.8 1.9 2.0 1.713 1.813 1.913 2.013 2.113 2.35 2.45 2.55 2.65 2.75 21E 22E 23E 24E 25E 2.1 2.2 2.3 2.4 2.5 2.201 2.301 2.401 2.501 2.601 2.70 2.80 2.90 3.00 3.10 21G 22G 23G 24G 25G 2.1 2.2 2.3 2.4 2.5 2.213 2.313 2.413 2.513 2.613 2.75 2.85 2.95 3.05 3.15 21J 22J 23J 24J 25J 2.1 2.2 2.3 2.4 2.5 2.213 2.313 2.413 2.513 2.613 2.85 2.95 3.05 3.15 3.25 26E 27E 28E 29E 30E 2.6 2.7 2.8 2.9 3.0 2.701 2.801 2.901 3.001 3.101 3.20 3.30 3.40 3.50 3.60 26G 27G 28G 29G 30G 2.6 2.7 2.8 2.9 3.0 2.713 2.813 2.913 3.013 3.113 3.25 3.35 3.45 3.55 3.65 26J 27J 28J 29J 30J 2.6 2.7 2.8 2.9 3.0 2.713 2.813 2.913 3.013 3.113 3.35 3.45 3.55 3.65 3.75 31E 32E 33E 34E 35E 3.1 3.2 3.3 3.4 3.5 3.201 3.301 3.401 3.501 3.601 3.70 3.80 3.90 4.00 4.10 31G 32G 33G 34G 35G 3.1 3.2 3.3 3.4 3.5 3.213 3.313 3.413 3.513 3.613 3.75 3.85 3.95 4.05 4.15 31J 32J 33J 34J 35J 3.1 3.2 3.3 3.4 3.5 3.213 3.313 3.413 3.513 3.613 3.85 3.95 4.05 4.15 4.25 36E 37E 38E 39E 40E 3.6 3.7 3.8 3.9 4.0 3.701 3.801 3.901 4.001 4.101 4.20 4.30 4.40 4.50 4.60 36G 37G 38G 39G 40G 3.6 3.7 3.8 3.9 4.0 3.713 3.813 3.913 4.103 4.113 4.25 4.35 4.45 4.55 4.65 36J 37J 38J 39J 40J 3.6 3.7 3.8 3.9 4.0 3.713 3.813 3.913 4.103 4.113 4.35 4.45 4.55 4.65 4.75 41E 42E 43E 44E 45E 4.1 4.2 4.3 4.4 4.5 4.201 4.301 4.401 4.501 4.601 4.70 4.80 4.90 5.00 5.10 41G 42G 43G 44G 45G 4.1 4.2 4.3 4.4 4.5 4.213 4.313 4.413 4.513 4.613 4.75 4.85 4.95 5.05 5.15 41J 42J 43J 44J 45J 4.1 4.2 4.3 4.4 4.5 4.213 4.313 4.413 4.513 4.613 4.85 4.95 5.05 5.15 5.25 a See Clause c) © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Table — Bearing length L, clamping length M and overall length E Part No /4 in UNF aL M +0 –0.03 E +0.04 –0 in in in /16 in UNF aL M +0 –0.03 in in Part No E +0.04 –0 Part No in /8 in UNF M +0 –0.03 E +0.04 –0 in in in aL 46E 47E 48E 49E 50E 4.6 4.7 4.8 4.9 5.0 4.701 4.801 4.901 5.001 5.101 5.20 5.30 5.40 5.50 5.60 46G 47G 48G 49G 50G 4.6 4.7 4.8 4.9 5.0 4.713 4.813 4.913 5.013 5.113 5.25 5.35 5.45 5.55 5.65 46J 47J 48J 49J 50J 4.6 4.7 4.8 4.9 5.0 4.713 4.813 4.913 5.013 5.113 5.35 5.45 5.55 5.65 5.75 51E 52E 53E 54E 5.1 5.2 5.3 5.4 5.201 5.301 5.401 5.501 5.70 5.80 5.90 6.00 51G 52G 53G 54G 5.1 5.2 5.3 5.4 5.213 5.313 5.413 5.513 5.75 5.85 5.95 6.05 51J 52J 53J 54J 5.1 5.2 5.3 5.4 5.213 5.313 5.413 5.513 5.85 5.95 6.05 6.15 a /16 in UNF /2 in UNF 2L 3L 4L 5L 0.2 0.3 0.4 0.5 0.330 0.430 0.530 0.630 1.05 1.15 1.25 1.35 3N 4N 5N 0.3 0.4 0.5 0.430 0.530 0.630 1.25 1.35 1.45 6L 7L 8L 9L 10L 0.6 0.7 0.8 0.9 1.0 0.730 0.830 0.930 1.030 1.130 1.45 1.55 1.65 1.75 1.85 6N 7N 8N 9N 10N 0.6 0.7 0.8 0.9 1.0 0.730 0.830 0.930 1.030 1.130 1.55 1.65 1.75 1.85 1.95 11L 12L 13L 14L 15L 1.1 1.2 1.3 1.4 1.5 1.230 1.330 1.430 1.530 1.630 1.95 2.05 2.15 2.25 2.35 11N 12N 13N 14N 15N 1.1 1.2 1.3 1.4 1.5 1.230 1.330 1.430 1.530 1.630 2.05 2.15 2.25 2.35 2.45 16L 17L 18L 19L 20L 1.6 1.7 1.8 1.9 2.0 1.730 1.830 1.930 2.030 2.130 2.45 2.55 2.65 2.75 2.85 16N 17N 18N 19N 20N 1.6 1.7 1.8 1.9 2.0 1.730 1.830 1.930 2.030 2.130 2.55 2.65 2.75 2.85 2.95 21L 22L 23L 24L 25L 2.1 2.2 2.3 2.4 2.5 2.230 2.330 2.430 2.530 2.630 2.95 3.05 3.15 3.25 3.35 21N 22N 23N 24N 25N 2.1 2.2 2.3 2.4 2.5 2.230 2.330 2.430 2.530 2.630 3.05 3.15 3.25 3.35 3.45 26L 27L 28L 29L 30L 2.6 2.7 2.8 2.9 3.0 2.730 2.830 2.930 3.030 3.130 3.45 3.55 3.65 3.75 3.85 26N 27N 28N 29N 30N 2.6 2.7 2.8 2.9 3.0 2.730 2.830 2.930 3.030 3.130 3.55 3.65 3.75 3.85 3.95 See Clause c) © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Table — Bearing length L, clamping length M and overall length E Part No /16 in UNF aL M +0 –0.03 E +0.04 –0 in in in Part No /2 in UNF aL M +0 –0.03 E +0.04 –0 in in in 31L 32L 33L 34L 35L 3.1 3.2 3.3 3.4 3.5 3.230 3.330 3.430 3.530 3.630 3.95 4.05 4.15 4.25 4.35 31N 32N 33N 34N 35N 3.1 3.2 3.3 3.4 3.5 3.230 3.330 3.430 3.530 3.630 4.05 4.15 4.25 4.35 4.45 36L 37L 38L 39L 40L 3.6 3.7 3.8 3.9 4.0 3.730 3.830 3.930 4.030 4.130 4.45 4.55 4.65 4.75 4.85 36N 37N 38N 39N 40N 3.6 3.7 3.8 3.9 4.0 3.730 3.830 3.930 4.030 4.130 4.55 4.65 4.75 4.85 4.95 41L 42L 43L 44L 45L 4.1 4.2 4.3 4.4 4.5 4.230 4.330 4.430 4.530 4.630 4.95 5.05 5.15 5.25 5.35 41N 42N 43N 44N 45N 4.1 4.2 4.3 4.4 4.5 4.230 4.330 4.430 4.530 4.630 5.05 5.15 5.25 5.35 5.45 46L 47L 48L 49L 50L 4.6 4.7 4.8 4.9 5.0 4.730 4.830 4.930 5.030 5.130 5.45 5.55 5.65 5.75 5.85 46N 47N 48N 49N 50N 4.6 4.7 4.8 4.9 5.0 4.730 4.830 4.930 5.030 5.130 5.55 5.65 5.75 5.85 5.95 51L 52L 53L 54L 5.1 5.2 5.3 5.4 5.230 5.330 5.430 5.530 5.95 6.05 6.15 6.25 51N 52N 53N 54N 5.1 5.2 5.3 5.4 5.230 5.330 5.430 5.530 6.05 6.15 6.25 6.35 a See Clause c) © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Appendix A Principles of flushness control and recommended gauging practice A.1 The major requirement of the user of a countersunk head bolt is that the upper surface of the head should fit with as great a degree of flushness as possible with the surface into which it is inserted This flushness is dependent upon both the tolerance on the head of the bolt and that on the countersunk hole into which the head is fitted The method of dimensioning adopted in this standard directly controls the flushness accuracy of the bolt in relation to the countersink, the result in an actual assembly being dependent upon the tolerance applied to the countersink, which is outside the scope of this standard A.2 In the traditional method of dimensioning countersunk head bolts, the limits on the bolt head thickness are affected by the tolerance on the shank diameter This however is of no consequence in the matter of flushness and it would be necessary for any degree of flushness to exercise a closer control on head thickness and/or shank diameter if the traditional dimensioning methods were used A.3 The recommended methods of gauging flushness are simple and not call for any measurement of difficult or dubious dimensions A.4 The most important aspect of the bolt head in the attainment of flushness is the position of the flat upper surface of the head in relation to the conical under surface The gauging dimension by which this is controlled is that between the flat upper surface and a plane which cuts the conical surface normal to its axis at a specified diameter known as the gauging diameter (see Figure 2) The dimension measured is known as the “head protrusion” and its tolerance as the “flushness tolerance” A.5 The variables which affect the flushness tolerance are: a) The diameter to sharp corners (the hypothetical intersection of the flat upper surface and the conical under surface of the head) and b) The included angle of the head The gauging diameter is at approximately one-third of the head depth from the upper surface 10 A.6 The elements which define the bolt head and which are required to be controlled by inspection are: a) head protrusion, the limits of which define the flushness tolerance; b) diameter of head to sharp corners; this is controlled indirectly by the inspection of a and d c) actual diameter of head for which a minimum is specified and which is the diameter at the land; d) included angle of the conical under surface; e) radius between conical surface and shank It is not a requirement of this standard that a particular method of inspection shall be employed Head protrusion may be checked by means of a gauge of the type shown in Figure 4, by a GO — NOT GO gauge, by optical projection, or by any other suitable means The actual diameter may be checked by direct measurement or by a GO — NOT GO gauge The head angle and radius at shank may be checked by optical projection A.7 Figure illustrates a type of gauge which has achieved some popularity for use with aircraft countersunk head bolts and rivets in the U.S.A Details of a suitable gauge block are given in Figure The intersection of the hole X with the top surface of the gauge block forms the diameter on which the cone of the bolt head rests The diameter of the hole X is slightly less than the gauging diameter N to permit the edge of the hole to be broken to form a land approximately 0.003 inch wide by lapping with a hardened steel ball until the dimension Z is within the stated limits The dimension Z is calculated from the formula: When the bolt is inserted in the block, the dial indicator is used to give a direct reading of head protrusion which is the amount by which the top surface of the bolt head protrudes above the top surface of the gauge block © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Figure — Method of measurement of head protrusion © The British Standards Institution 2012 11 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Figure — Protrusion gauge block (see Figure and Appendix A.7) Nominal size of bolt Ball dia Y Nominal Counter bore Dia X Ball protrusion Za +0 –0.001 +0.0002 –0 in No 8-32 UNC No 10-32 UNF /4 in UNF 5/ 16 in UNF /8 in UNF /16 in UNF /2 in UNF a (13/32) (15/32) (21/32) (13/16) 0.40625 0.46875 0.65625 0.81250 1.00000 (1) 1.18750 (13/16) 1.31250 (15/16) 0.263 0.311 0.420 0.535 0.649 0.764 0.878 Depth of counter bore T +0.010 –0 in 0.3562 0.4081 0.5783 0.7103 0.8786 1.0468 1.1422 in 0.120 0.120 0.120 0.150 0.170 0.200 0.230 Dia of guide W Length of guide S +0.001 –0 ± 0.010 in 0.1665 0.1935 0.2535 0.3160 0.3785 0.4420 0.5045 in 0.25 0.30 0.40 0.50 0.60 0.70 0.80 For the basis of calculation of this dimension see Appendix A.7 12 © The British Standards Institution 2012 ������������������������ ��������� ���� BS 2A 173:1962+A7:2012 Appendix B Table for conversion of inches to approximate millimetre equivalents in mm in mm 1/ /16 /8 7/ 16 6.4 7.9 9.5 11.1 25.4 50.8 76.2 101.6 /2 /16 5/ /4 12.7 14.3 15.9 19.1 127.0 152.4 177.8 203.2 /8 22.2 10 228.6 254.0 © The British Standards Institution 2012 173:1962 BS 2A 173: +A7:2012 1962 BSI — British Standards Institution BSI is the independent national body responsible for preparing British Standards It presents the UK view on standards in Europe and at the international level It is incorporated by Royal Charter Revisions British Standards are updated by amendment or revision Users of British Standards should make sure that they possess the latest amendments or editions It is the constant aim of BSI to improve the quality of our products and services We would be grateful if anyone finding an inaccuracy or ambiguity while using this British Standard would inform the Secretary of the technical committee responsible, the identity of which can be found on the inside front 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