ASME B1.21:1997 pdf download METRIC SCREW THREADS M J PROFllE
1 GENER AL
1.1 Scope This Standard establishes the basic triangular profile for the MJ thread form; provides a system of designa- tions; lists the standard series of diametedpitch combina- tions for diameters from 1.6 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 I. 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 be 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 at minimum material condition. Additional Tolerance Classes 6H/6g 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 threads in ASME B 1.13M. Classes 6W6g 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 l. 13M) and the MJ profile are not interchangeable because of possible interference between the MJ external thread minor diameter and the B I . 13M internal thread minor diameter. However, the MS internal thread will assemblewith the Bl.13M external thread.
1.4 Federal Government Use
When this Standard is approved by the Departmentof Defense and Federal Agencies and is incorporatedinto FED-STD-H28/21，Screw Thread Standards forFederal Services. Section 2l. the use of this Standardby the Federal Govermment is subject to all the requirements and limitations of FED-STD-H28/21.
1.5 References
The latest issues of the following documents forma part of this Standard to the extent specified herein.American National StandardsASME B1.3M，Screw Thread Gaging Systems forDimensional Acceptability — Inch and Metric ScrewThreads (UN，UNR，UNJ，M，and MJ)ANSI/ASME B1.7M，Nomenclature，Definitions，andL.etter Symbols for Screw ThreadsASME BI.10M，Unified Miniature Screw ThreadsASME B1.13M，Metric Screw Threads – M ProfileASME B1.15, Unified Inch Screw Threads (UNJ ThreadForm)ANSI/ASME BI.22M,Gages and Gaging Practice forM] Series Metric Screw ThreadsASME B1.30M，Screw Threads — Standard Practicefor Calculating and Rounding Dimensions
ISO Standards
ISO 261, ISO General Purpose Metric Screw Threads –General PlanISO 965-1，ISO General Purpose Metric ScrewThreads – Part I Principles and Basic DataISO 5855-1-2-3，Aerospace MJ Threads
ASME B1.21:1997 pdf download
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