1、 Intentionally left blank The American Society of Mechanical Engineers AN AMERICAN NATIONAL STANDARD METRIC SCREW THREADS I I M J PROFllE ASME B1.21 M-1 NU7 (Revision of ANSI B1.21 M-1178) Date of Issuance: April 2, 1998 This Standard will be revised when the Society approves the issuance of a new e
2、dition. 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 procedures accredited as meeting the criteria for Ameri
3、can National Standards. The Consensus 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 o
4、pportunity 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 asser
5、ted 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 the determination of t
6、he validity of any such patent rights, and the risk of the 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 standar
7、d. ASME accepts responsibilityfor only those interpretations issued in accordance with governing ASME procedures and policies which preclude the issuance of interpretations by individual volunteers. No part of this document may be reproduced in any form, in an electronic retrieval system or otherwis
8、e, without the prior written permission of the publisher. The American Society of Mechanical Engineers 345 East 47th Street, New York, NY 10017 Copyright 0 1998 by THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All Rights Reserved Printed in U.S.A. (This Foreword is not part of ASME B1.21M-1997.) This
9、 Metric Screw Thread Standard, MJ Profile, is a hard metric version similar to the UNJ Inch ASME BI .15 and MIL-S-8879 Standards which have a 0.1501 1P to 0.18042P controlled radius root in the external thread and the internal thread minor diameter truncated to accommodate the external thread maximu
10、m root radius. This metric thread is recommended for use in high temperature or high fatigue applications. Tolerance Class 4H5W4h6h is approximately equivalent to a Class 3M3B Inch J Thread and is intended for aerospace applications. Tabulated data has been provided for Tolerance Class 4g6g and 4G6G
11、/4G5G for commercial applications or when the standard reduction for coating or plating provided in this Standard is not adequate for the coating thickness required. Table 6 in this issue has been added to define limiting dimensions for Tolerance Class 6g/6H for commercial producers and users of thi
12、s class. Tolerance Class 6g/6H is intended for use only in commercial applications. This metric Standard has as its original basis the work done under the direction of the SAE E21E25 Metric Thread Panel, which developed and published SAE Aerospace Standard AS 1370. A replica of AS 1370 was ballot ci
13、rculated in American National Standards Institute Committee B 1 as ANSI B1.21. Since the UNJ inch screw thread is predominantly used in aerospace designs, the aerospace industry decided to produce a hard metric version for aerospace metric design. The MJ screw thread project was initiated by SAE Com
14、mittee E21, which was responsible for aerospace propulsion design standards. At the Committees October 25, 1971 meeting, Project E21-122 was established to develop metric screw thread requirements for metric aerospace fasteners and threaded parts. A metric thread panel was organized to include repre
15、sentation from throughout the aerospace industry. Participating organizations included the following: SAEIE21 - Aerospace Propulsion Design Standards SAEE25 - Aerospace Propulsion Utility Parts Standards AIAAVASC - National Aerospace Standards Committee (airframe) ATA - Air Transport Association SBA
16、C - Society of British Aircraft Constructors ALMA - American Locknut Manufacturers Association APFA - Aerospace Precision Fastener Association ASDNPAFB - Aeronautical Systems Division, U.S. Air Force NAPTC - Naval Air Propulsion Test Center, U.S. Navy Liaison representation from ANSYOMFS This Panel
17、took into account the activities of ANSVOMFS, SBAC, ATA, AECMA, ISO/ TC 20/SC 4, and ISO/TC I/SC 5 in order to reflect agreements compatible with international and U.S. aerospace metric screw thread requirements, as well as coordinating with ANSI/ OMFS requirements. . 111 Much work was done in devel
18、oping surveys and drafts which were ballot circulated throughout the aerospace industry for resolving the thread design elements and involved the following: (a) metric diametedpitch combinations for aerospace fasteners, (6) metric diametedpitch combinations for other aerospace parts, (c) thread desi
19、gn form, and (d) thread tolerance class and formulae. After fourteen meetings of the Metric Thread Panel, including special meetings with OMFS and the military, the aerospace industry ballot circulated the AS 1370 MJ Metric Screw Thread Standard for approval. In May 1976, it was approved and publish
20、ed by the SAE Aerospace Council. In addition, two preliminary documents were also published. AS 1337, published in March 1974, lists the aerospace diametedpitch combinations for threaded fasteners, and AS 1338, published in February 1976, documents the MJ profile requirements and tolerance class. Fo
21、llowing the publication of AS 1370, an additional standard, AS 1421 - listing aerospace diametedpitch combinations for shaft or bearing retaining screw threads - was published in August 1976. The International Organization for Standardization Subcommittee for Aerospace Bolts and Nuts, ISO/TC 20/SC 4
22、, has accepted the MJ metric thread profile for aerospace metric threaded fasteners. AS 1370 is serving as the basis for establishing the IS0 International Standard for MJ metric screw threads. Upon publication of AS 1370, SAE agreed to submit this Standard to ANSI Committee B1 for approval as the A
23、merican National Standard for MJ metric screw threads. ANSI B1.21 was approved by American National Standards Committee B1 on February 23, 1977. The proposed Standard was submitted by Standards Committee B1 to the Secretariat and ANSI. It was approved and formally designated an American National Sta
24、ndard on November 21, 1978. This issue updates the 1978 issue and includes: (a) the addition of Tolerance Class 4G6G and 4G5G/4g6g to be comparable with ASME B1.15, Unified Inch Screw Threads (UNJ Thread Form), which includes Class 2 UNJ Threads; (b) the addition of Tolerance Class 6W6g to provide a
25、 Metric J profile comparable with ASME B 1.13M, Metric Screw Threads - M Profile, for use in general applications; and (c) changes in rounding procedures which follow the principles of ASME B1.30M. Suggestions for improvement of this Standard are welcome. They should be sent to Secretary, ASME B 1 S
26、tandards Committee, 345 East 47th Street, New York, NY 10017. ASME B 1.2 1 M- 1997 was approved as an American National Standard on December 9, 1997. iv ASME STANDARDS COMMITTEE B1 Standardization and Unification of Screw Threads (The following is the roster of the Committee at the time of approval
27、of this Standard.) OFFICERS A. D. Shepherd, Jr., Chair D. S. George, Vice Chair G. L. Fechter, Secretary COMMITTEE PERSONNEL J. R. Anderson, Delphi Harrison Thermal System, Lockport, New York A. L. Barrows, Greenfield Industries, Greenfield, Massachusetts M. H. Bernier, Pilgrim Screw Corp., Providen
28、ce, Rhode Island J. M. Bobelak, McDonnell Douglas Corp., St. Louis, Missouri D. P. Cadieux, Glastonbury Gage, Glastonbury, Connecticut F. G. Calderone, Quality Systems Implementers, Troy, Ohio J. Davis, US. NRC, Washington, D.C. L. N. Dixon, Jr., General Electric, Cincinnati, Ohio R. Dodge, Pennoyer
29、-Dodge Co., Glendale, California A. E. Ellis, Consultant, Bedford, Massachusetts G. L. Fechter, The American Society of Mechanical Engineers, New York, New York R. E. Ferry, Jr., R. B. provides a system of designa- tions; lists the standard series of diametedpitch combina- tions for diameters from 1
30、.6 to 200 mm; and specifies limiting dimensions and tolerances. It specifies the characteristics of the MJ metric series of threads having a minimum 0.1501 1P radius at the root of the external thread, and also having the minor diameter of the external and internal threads increased above the ASME B
31、 1.13M thread form to accommodate the external thread root radius. 1.2 Field of Application The MJ screw thread is designed for use on highly stressed applications requiring high fatigue strength. For aerospace applications, except for fluid fittings, Tolerance Classes 4H5H or 4G6G and 4h6h should b
32、e used. These classes approximate Classes 3B/3A in the inch system. Aerospace fluid fittings use Classes 4H5H or 4H6H and 4g6g. Tolerance Classes 4G5G or 4G6G and 4g6g are provided for use when thread allowances are required. These classes result in a slightly tighter fit than the inch Classes 2B/2A
33、 at minimum material condition. Additional Tolerance Classes 6W6g are included in this Standard to provide appropriate product selection based on general applications. These classes and the selection of standard diametedpitch combinations are the same as those provided for the M profile metric screw
34、 threads in ASME B 1.13M. Classes 6H/6g result in a slightly looser fit than inch Classes 2B/2A at minimum material condition. 1.3 Assembly Threads conforming to the M profile (ASME B I. 13M) and the MJ profile are not interchangeable because of possible interference between the MJ external thread m
35、inor diameter and the 3 1.13M internal thread minor diameter. However, the MJ internal thread will assemble with the B 1.13M external thread. 1.4 Federal Government Use When this Standard is approved by the Department of Defense and Federal Agencies and is incorporated into FED-STD-H28/2 1, Screw Th
36、read Standards for Federal Services, Section 21, the use of this Standard by the Federal Government is subject to all the require- ments and limitations of FED-STD-H28/2 1. 1.5 References The latest issues of the following documents form a part of this Standard to the extent specified herein. Americ
37、an National Standards ASME B 1.3M, Screw Thread Gaging Systems for Dimensional Acceptability - Inch and Metric Screw Threads (UN, UNR, UNJ, M, and MJ) ANSVASME B 1.7M, Nomenclature, Definitions, and Letter Symbols for Screw Threads ASME Bl.lOM, Unified Miniature Screw Threads ASME B1.13M, Metric Scr
38、ew Threads - M Profile ASME B 1.15, Unified Inch Screw Threads (UNJ Thread ANSVASME B1.22M, Gages and Gaging Practice for ASME B 1.30M, Screw Threads - Standard Practice Form) MJ Series Metric Screw Threads for Calculating and Rounding Dimensions IS0 Standards IS0 26 1, IS0 General Purpose Metric Sc
39、rew Threads - General Plan IS0 965-1, IS0 General Purpose Metric Screw Threads - Part 1 Principles and Basic Data IS0 5855-1-2-3, Aerospace MJ Threads 2 PROFILE OF THREAD 2.1 Basic Profile The basic profile is the theoretical profile correspond- ing to the basic dimensions of the thread major diamet
40、er, I ASME B1.21M-1997 METRIC SCREW THREADS: MJ PROFILE -P- i FIG. 1 BASIC PROFILE pitch diameter, and minor diameter. The profile applies in an axial plane and is shown in Fig. I. 2.2 Basic Thread Profile Symbols The symbols used in the basic profile shown in D bsc = basic major diameter of interna
41、l thread D2 bsc = basic pitch diameter of internal thread Dl bsc = basic minor diameter of internal thread d bsc = basic major diameter of external thread d2 bsc = basic pitch diameter of external thread dl bsc = basic minor diameter of external thread Fig. I represent the following: H = height of f
42、undamental triangle P = pitch Appendix B provides a complete list of symbols applicable to the MJ thread form. 2.3 Design Profiles The design profile for the internal thread at maximum material condition is the same as the basic profile, except in practice, the root is cleared above the basic major
43、diameter, D bsc. See Fig. 2. The design profile for the external thread at maximum material condition for Tolerance Position h is the basic profile with a radiused minor diameter tangent to the 2 N F 0 -+ t of thread flanks for the upper limit profile. For Tolerance Position g, an allowance is appli
44、ed to the basic profile. The external thread crest may be flat, partially or comer rounded, tangent to the 0.125P flat. See Fig. 3. (Refer- ence also para. 4.2, Tolerance System.) 2.4 Root Radius of the Thread 2.4.1 Internal Thread. For internal threads, the profile of the actual root of the thread
45、shall at no point transgress the basic profile. No root radius is specified. 2.4.2 External Thread. For external threads, the profile of the actual root of the thread shall lie within the root radius tolerance zone shown in Fig. 4. The limit dimensions of the root radius R, as shown in Fig. 4, and t
46、heir values are specified in Table 1. The profile shall be a continuous smoothly blended non- reversing curve, no part of which shall have a radius of less than 0.1501 If and which is tangent to the thread flanks at not less than 0.56258 basic thread depth. The profile may comprise tangent flank cir
47、cular arcs that are tangent to the flanks and a flat at the minor diameter provided that the minor diameter, d3, is within the zone established in Fig. 4. 2 METRIC SCREW THREADS: MJ PROFILE ASME B1.21M-1997 x E s 2 a“ x I FIG. 2 INTERNAL THREAD TOLERANCES 2.4.3 Incomplete Threads. Unless otherwise s
48、pecified, the runout threads on externally threaded parts shall be no less than one, nor more than two pitches in length. The threads shall runout onto the shank without any abrupt change in cross-sectional area. The root radius shall be no less than the minimum radius of the full thread section. 3
49、SERIES OF THREADS This Standard includes a selected series of threads extracted from IS0 261 plus some additional sizes in the constant pitch series. Also, it includes the standard series of diametedpitch combinations for aerospace screws, bolts and nuts, aerospace fluid system fittngs, and other preferred screw threads. See Tables 2, 3, 4, and 5. Table 6 has been added to define the limiting dimen- sions for Tolerance Classes 6W6g. A very limited selection of standard sizes has been extracted from IS0 261. This
