METRIC
SCREW THREADS: MJ PROFILE
(Revision of ANSI B1.21M-1978)
REAFFIRMED2018
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METRIC SCREWTHREADS: MJPROFILE
This Standard will be revised when the Society approves the issuance ofrequirements of this Standard issued to this edition.
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FOREWORD
(This Foreword is not part of ASME B1.21M-1997.)
This Metric Screw Thread Standard MJ Profil is a hard metric version similar to theUNJ Inch ASME B1.15 and M1L-S-8879 Standards which have a 0.15011P to 0.18042P controlled radius root in the extemal thread and the intermal thread minor diameter truncatede to acmodate the extermal thread maximum root radius. This metric thread is remended
Tolerancc Class 4H5H/4h6h is approximately equivalent to a Class 3A/3B Inch J Thread
Tabulated data has been provided for Tolerance Class 4g6g and 4G6G/4GSG for mercialis not adequate for the coating thickness required. applications or when the standard reduction for coating or plating provided in this Standard
Table 6 in this issue has been added to define limiting dimensions for Tolerance Class6g/6H for mercial producers and users of this class. Tolerance Class 6g/6H is intended for use only in mercial applications.
SAE E21/E25 Metric Thread Panel which developed and published SAE Aerospace Standard This metric Standard has as its original basis the work done under the direction of theAS 1370. A replica of AS 1370 was ballot circulated in American National StandardsInstitute Committee B1 as ANSI B1.21.
Since theUNJ inch screw thread is predominantly used in aerospace designs theaerospacescrew thread project was initiated by SAE Commitee E21 which was responsible for industry decided to produce a hard metric version for aerospace metric design. The MJaerospace propulsion design standards. At the Commitee's October 25 1971 meeting.aerospace fasteners and threaded parts.
aerospace industry. Participating organizations included the following: A metric thread panel was organized to include representation from throughout the
SAE/E21 - Aerospace Propulsion Design StandardsSAE/E25 -Aerospace Propulsion Utility Parts StandardsAIA/NASC - National Aerospace Standards Committee (airframe) ATAAir Transport AssociationSBAC -Society of British Aircraft Constructors ALMA - American Locknut Manufacturers AssociationAPFA Aerospace Precision Fastener AssociationNAPTC - Naval Air Propulsion Test Center U.S. Navy ASD/WPAFB -Aeronautical Systems Division U.S. Air ForceLiaison representation from ANSI/OMFS
TC 20/SC 4. and ISO/TC 1/SC 5 in order to reflect agreements patible with intemational This Panel took into account thc activities of ANSI/OMFS SBAC ATA AECMA ISO/and US. aerospace metric screw thread requirements as well as coordinating with ANSI/ OMFS requirements.
