A N A M E R I C A N N A T I O N A L S T A N D A R D Screw Threads Nomenclature, Definitions, and Letter Symbols ASME B1 7 2006 (Revision of ANSI/ASME B1 7M 1984) C opyrighted m aterial licensed to S t[.]
(Revision of ANSI/ASME B1.7M-1984) Screw Threads: Nomenclature, Definitions, and Letter Symbols A N A M E R I C A N N AT I O N A L STA N DA R D Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled when printed ASME B1.7-2006 (Revision of ANSI/ASME B1.7M-1984) Screw Threads: Nomenclature, Definitions, and Letter Symbols AN AMERICAN NATIONAL STANDARD Three Park Avenue • New York, NY 10016 Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled wh ASME B1.7-2006 This Standard will be revised when the Society approves the issuance of a new edition There will be no addenda or written interpretations of the requirements of this Standard issued to this edition ASME is the registered trademark of The American Society of Mechanical Engineers This code or standard was developed under the procedures accredited as meeting the criteria for American National Standards The Standards Committee that approved the code or standard was balanced to assure that individuals from competent and concerned interests have had an opportunity to participate The proposed code or standard was made available for public review and comment, which provides an opportunity for additional public input from industry, academia, regulatory agencies, and the public-at-large ASME does not “approve”, “rate,” or “endorse” any item, construction, proprietary device, or activity ASME does not take any position with respect to the validity of any patent rights asserted in connection with any items mentioned in this document, and does not undertake to insure anyone utilizing a standard against liability for infringement of any applicable letters patent, nor assumes any such liability Users of a code or standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, is entirely their own responsibility Participation by federal agency representative(s) or person(s) affiliated with industry is not to be interpreted as government or industry endorsement of this code or standard ASME accepts responsibility for only those interpretations of this document issued in accordance with the established ASME procedures and policies, which precludes the issuance of interpretations by individuals No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher The American Society of Mechanical Engineers Three Park Avenue, New York, NY 10016-5990 Copyright © 2006 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All rights reserved Printed in U.S.A Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled wh Date of Issuance: November 17, 2006 Foreword Committee Roster v vi General Definition of Terms Figures Allowance Axis of Thread Best Wire Size Blunt Start Thread Bottom of Chamfer Clearance Flank Countersink Crest Root and Crest Truncation 10 Fundamental Deviation 11 Metric Tolerance System for Screw Threads 12 Element 13 Flank 14 Flank Angle 15 Flat Form 16 Following Flank 17 Gauge Plane 18 Height of Fundamental Triangle 19 Height of Thread 20 Height of Thread Engagement 21 Helix 22 Helix Variation (Drunken Thread) 23 Incomplete Thread 24 Interference Fit 25 Internal Thread 26 Lead 27 Leading Flank 28 Gaging Length 29 Length of Assembly 30 Length of Thread Engagement 31 Load Flank 32 Major Clearance 33 Major Diameter, External Thread 34 Major Diameter, Internal Thread 35 Major Diameter, Internal Thread (Rounded Form) 36 Major Diameter, Taper Thread 37 Minor Clearance 38 Minor Diameter, External Thread (Flat Form) 39 Minor Diameter, External Thread (Rounded Form) 40 Minor Diameter, Internal Thread 41 Minor Diameter, Taper Thread 42 Multiple Start Thread iii 2 4 4 7 7 8 9 9 10 11 11 11 11 11 11 12 12 12 12 12 12 12 13 14 14 14 14 14 Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled wh CONTENTS Pitch Pitch Cone Pitch Cylinder Pitch Diameter, External Thread Pitch Diameter, Internal Thread Plane of Vanish Point Profile, Basic Thread Root Radius Screw Thread Sharp Crest and Root Shear Area Straight Thread Thread Angle Thread Ridge Thickness Truncation Vanish Cone 14 14 14 15 15 15 16 16 16 16 17 18 23 23 23 24 19 20 21 22 Nonmandatory Appendices A Superseded Thread Series Designations B ISO Symbols for Screw Threads C Greek Alphabet 25 26 27 Tables General Symbols ISO General Symbols Thread Series Designations ISO Thread Series Designations iv Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled wh 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 The first revision of ASA B1.7-1949, the first American Standard on Nomenclature, Definitions, and Letter Symbols for Screw Threads, was approved in January 1965 These earlier definitions and symbols were subsequently published as appendix material in ASA B1.1, B2.1, and B2.2 As such they underwent some revision over the years A draft based on such revisions, dated July 1961, was prepared by Subcommittee and widely circulated by the sponsors for comment Extensive comments were received from members of Sectional Committee B1, B2, B4, and others, which were reviewed and acted upon at a meeting of Subcommittee 8, held November 28, 1961 A second revised draft, dated July 1962, was prepared and submitted to the American-BritishCanadian Conference on Engineering Standards, held in Harriman, New York on September 22–26, 1962 Suggested revisions agreed upon by the conference were embodied in the draft, which was then submitted to letter ballot by Sectional Committees B1 and B2 on July 9, 1963 Further refinements were made in the proposal because of comments received from the sectional committee ballots, and a new draft was issued in May 1964 The draft was submitted to the American Standards Association for approval and designation as an American Standard This was granted on January 19, 1965, and reaffirmed in 1972 by the American National Standards Institute as American National Standard ANSI B1.7 Following the 1972 reaffirmation, comments from members of the American National Standards Committee B1, and others, indicated that a complete revision be undertaken A new draft was prepared and submitted in March 1975 to Subcommittee for review and approval After numerous comments and subsequent changes, the proposed standard was submitted to and approved by American National Standards Committee B1 The document was then transmitted to the Secretariat and ANSI in October 1976 It was approved as an American National Standard, ANSI B1.7-1977, on September 16, 1977 Within the period from 1977 to 1984 there was considerable B1 standards activity in the development of metric screw thread standards for U.S usage ISO standards were blended with ANSI standards, requiring many revisions in ANSI symbology and definitions of terms ISO symbols were adopted, except those where a change from American practice would confuse the general understanding of the elements symbolized Also, many ISO definitions were incorporated into American definitions in order to facilitate the correct interpretation of both ISO and ANSI terminology These revisions were approved and designated as American National Standard ANSI/ASME B1.7M-1984, on November 2, 1984 Screw thread standards are constantly being revised as required by the ASME B1 Committee Additionally, the title of this document was changed to “Screw Threads: Nomenclature, Definitions, and Letter Symbols.” This revision was approved and designated by the American National Standards Institute on September 11, 2006 v Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled wh FOREWORD (The following is the roster of the Committee at the time of approval of this Standard.) STANDARDS COMMITTEE OFFICERS A L Barrows, Chair D S George, Vice Chair A L Guzman, Secretary STANDARDS COMMITTEE PERSONNEL A L Barrows, Kennametal, Inc F G Calderone, Corresponding Member, Quality Systems Implementers L N Dixon, Jr., General Electric R Dodge, Pennoyer-Dodge Co D Everett, National Institute of Standards and Technology G A Flannery, Corresponding Member, Mercury Gage Co H N Frost, Defense Supply Center J O Gehret III, Vermont Thread Gage, LLC D S George, Ford Motor Co J R Gervasi, Kerr Lakeside, Inc J Greenslade, Greenslade & Co L C Borowski, Alternate, Greenslade & Co A L Guzman, The American Society of Mechanical Engineers R J Hukari, SPS Technologies L C Johnson, The Johnson Gage Co D D Katz, Precision Fittings R P Knittel, Leitech-US Ltd P A Larouche, Swanson Tool Manufacturing B Larzelere, Corresponding Member, Deltronic Corp L L Lord, Corresponding Member, Consultant M H McWilliams, PMC Lonestar D R Maisch, Alternate, PMC Lonestar D Miskinis, Kennametal, Inc W R Newman, Corresponding Member, Consultant D R Oas, Seaway Bolt & Specials Corp M W Rose, Glastonbury Southern Gage W A Watts, Alternate, Glastonbury Southern Gage E Schwartz, Consultant R H Searr, Member Emeritus, Mak Tool & Gage B F Sheffler, Dresser-Rand Co A D Shepherd, Jr., Emuge Corp D Skierski, Sterling Gage & Calibration, LLC R D Strong, General Motors Vehicle Engineering Center A F Thibodeau, Member Emeritus, Swanson Tool Manufacturing, Inc R E Vincent, Jr., General Plug Manufacturing Co C J Wilson, Industrial Fasteners Institute SUBCOMMITTEE 7—NOMENCLATURE, DEFINITIONS, AND LETTER SYMBOLS FOR SCREW THREADS B F Sheffler, Chair, Dresser-Rand Co A L Barrows, Kennametal, Inc F G Calderone, Corresponding Member, Quality Systems Implementers L N Dixon, Jr., General Electric R Dodge, Pennoyer-Dodge Co D S George, Ford Motor Co J Jennings, Corresponding Member, Naval Surface Warfare Center L C Johnson, The Johnson Gage Co D D Katz, Precision Fittings R P Knittel, Leitech-US Ltd B Larzelere, Corresponding Member, Deltronic Corp W R Newman, Corresponding Member, Consultant M W Rose, Glastonbury Southern Gage E Schwartz, Consultant R H Searr, Member Emeritus, Mak Tool & Gage A D Shepherd, Jr., Emuge Corp R E Spencer, Faber Enterprises, Inc C J Wilson, Industrial Fasteners Institute vi Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled wh ASME B1 COMMITTEE Screw Threads SCREW THREADS: NOMENCLATURE, DEFINITIONS, AND LETTER SYMBOLS Publisher: International Organization for Standardization (ISO), rue de Varembé, Case Postal 56, CH-1211, Genève 20, Switzerland/Suisse GENERAL 1.1 Scope The purpose of this Standard is to establish a uniform practice for standard screw threads with regard to the following: (a) screw thread nomenclature (b) letter symbols for the designating features of a screw thread for use on drawings, in tables that set forth dimensional standards, in other records, and for expressing mathematical relationship This Standard consists of: a glossary of terms, illustrations, an illustrated table showing the application of symbols, and a table of thread series designations Many of the terms and symbols specified in this Standard vary considerably from those prior to the 1984 issue, because ISO terms and symbols have been adopted where the intended definition is the same 1.3 Federal Government Use When this Standard is approved by the Department of Defense and Federal agencies, and is incorporated into FED-STD-H28/1, Screw Thread Standards for Federal Services, Section 1, the use of this Standard by the Federal Government is subject to all requirements and limitations of FED-STD-H28/1 DEFINITION OF TERMS The definitions presented herein are listed alphabetically and apply generally to all forms of screw threads, thread gages, and thread measurements They relate to the following: (a) types of screw threads (b) size and fit of threaded parts in general (c) geometric elements, attributes, and dimensions of screw threads ISO nomenclature is used where the exact meaning is coincident with the U.S practice 1.2 References The following is a list of publications referenced in this Standard ANSI/CGA V-1, National Gas Screw Threads1 Publisher: Canadian Gas Association (CGA), 350 Sparks Street, Ottawa, Ontario K1R 7S8, Canada ASME B1.20.7, Hose Coupling Screw Threads ASME Y14.5M, Dimensioning and Tolerancing Publisher: The American Society of Mechanical Engineers (ASME), Three Park Avenue, New York, NY 10016-5990; Order Department: 22 Law Drive, P.O Box 2300, Fairfield, NJ 07007-2300 ISO 7-1, Pipe Threads Where Pressure Tight Joints are Made on Threads—Part 1: Designation, Dimensions, and Tolerances ISO 228-1, Pipe Threads Where Pressure Tight Joints are Not Made on the Threads—Part 1: Designation, Dimensions, and Tolerances ISO 1502, ISO General Purpose Metric Screw ThreadGauging ISO 2901, ISO Metric Trapezoidal Screw Threads ISO 2902, ISO Metric Trapezoidal Screw Threads ISO 2903, ISO Metric Trapezoidal Screw Threads ISO 2904, ISO Metric Trapezoidal Screw Threads ISO/R1501, ISO Miniature Screw Threads actual fit: the measured difference, subject to measurement uncertainty, before assembly, between the sizes of two mating parts that are to be assembled actual size: the measured size of a characteristic or element subject to measurement uncertainty addendum: the addendum of an external thread is the radial distance between the major and pitch cylinders or cones, respectively The addendum of an internal thread is the radial distance between the minor and pitch cylinders or cones, respectively This term applies to those threads having a recognized pitch cylinder or pitch cone allowance: a prescribed difference between the maximum material limits of mating parts It is the minimum clearance (positive allowance) or maximum interference (negative allowance) between such parts It is numerically equal to the absolute value of ISO term fundamental deviation (see Fig 1) attribute: nondimensional thread element(s) and characteristic(s), taken singly or in a group Inspection/evaluation by limit gages is an attribute inspection axis of thread: the axis of the thread pitch cylinder or cone (see Fig 2) May also be obtained from American National Standards Institute (ANSI), 25 West 43rd Street, New York, NY 10036 Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled wh ASME B1.7-2006 SCREW THREADS: NOMENCLATURE, DEFINITIONS, AND LETTER SYMBOLS Maximum material limit (minimum hole diameter) Hole Shaft Hole Maximum material limit (maximum shaft diameter) Negative Allowance (Minimum Hole Diameter – Maximum Shaft Diameter) Maximum material limit (minimum hole diameter) Hole Shaft Hole Maximum material limit (maximum shaft diameter) Positive Allowance (Minimum Hole Diameter – Maximum Shaft Diameter) Fig Allowance Axis Axis Fig Axis of Thread Best wire diameter Best wire diameter Pitch line j Basic pitch line Basic thread profile Nonsymmetrical Thread Symmetrical Thread Fig Best Wire Size 2j Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled wh ASME B1.7-2006 basic hole system: a system of fits in which the design size of the hole is the basic size, and the allowance, if any, is applied to the shaft External thread Internal thread basic profile of thread: see profile, basic thread Blunt start basic shaft system: a system of fits in which the design of the shaft is the basic size, and the allowance, if any, is applied to the hole basic size: that size from which the limits of size are derived by the application of allowances and tolerances best wire size: for symmetrical threads, the size of a wire that would touch at the pitch diameter on a basic profile thread of zero lead angle For nonsymmetrical threads, governed by ASME B1.9, the best wire size will contact the load flank at a point twice the distance above the pitch line that the contact point on the clearance flank is below the pitch line (see Fig 3) Fig Blunt Start Thread bilateral tolerance: a tolerance in which variation is equally larger and smaller than the specified dimension bilateral tolerance system: a design plan that uses only bilateral tolerances complete thread: thread(s) whose profile lies within the size limits See also effective thread and length of complete thread black crest thread: a thread whose crest displays the unfinished cast, rolled, or forged surface NOTE: In pipe threads terminology, this was formerly referred to as the perfect thread, but that term is no longer considered desirable blunt start thread: a thread with removal of the incomplete thread at the starting end (see Fig 4) This is a feature of the threaded parts that are repeatedly assembled by hand, such as hose couplings and thread gages, to prevent cutting of hands and crossing of threads Also known as Higbee cut or a convoluted thread concentricity: twice the value of eccentricity convoluted thread: see blunt start thread countersink: a bevel or flare at the end of a hole (see Fig 7) bottom of chamfer: the intersection of the chamfer cone and the pitch cone of an internal taper pipe thread (see Fig 5) crest: the surface of a thread that joins the flanks of the same thread, and is farthest from the cylinder or cone from which the thread projects (see Fig 8) chamfer: a conical surface at the starting end of a thread crest apex: see sharp crest characteristic: the quality(s), peculiarity(s), or feature(s) that is a conspicuous or prominent detail(s) of the thread See also attribute and element crest diameter: the diameter of an imaginary cylinder or cone bounding the crest of a screw thread This is the major diameter of an external thread and minor diameter of an internal thread class of thread: an alphanumerical designation to indicate the standard grade of tolerance and allowance specified for a thread (e.g., 2A, 2B) crest truncation: the crest truncation of a thread is the radial distance from the sharp crest (crest apex) and the cylinder or cone that would bound the crest (see Fig 9) clearance fit: a fit between mating assembled parts that provides a clearance at their maximum material condition crest width: the distance between the points of intersection of the flanks of the thread ridge and the imaginary cylinder defined by the crest diameter (see Fig 9) clearance flank: the flank that does not take the externally applied axial load in an assembly (see Fig 6) coated thread: a thread with one or more applications of additive material This includes dry film lubricants, but excludes soft or liquid lubricants that are readily displaced in assembly and gaging Plating and anodizing are included as coatings cumulative form variation: the combined effect on functional size of individual thread variations in lead (pitch), helix, flank angle, taper, and roundness It is the maximum difference between GO functional diameter size and pitch diameter size taken along and around the axis of the usable thread common boundary: the portion of the basic profile common to the maximum material conditions of the external and internal threads Violation of the common boundary produces interference cumulative pitch: the distance measured parallel to the axis of the thread between corresponding points on any two threads Copyrighted material licensed to Stanford University by Thomson Scientific (www.techstreet.com), downloaded on Oct-05-2010 by Stanford University User No further reproduction or distribution is permitted Uncontrolled wh ASME B1.7-2006 SCREW THREADS: NOMENCLATURE, DEFINITIONS, AND LETTER SYMBOLS