Metric Screw Threads MJ Profile Machinery's Handbook, 31st Edition
2034
Examples:
External thread M6.5 × 1 − 4h6h − SPL (22) Major dia = 6.320 − 6.500 Pitch dia = 5.779 − 5.850 Minor dia = 5.163 − 5.386
Internal thread M6.5 × 1 − 4H5H − SPL (23) Major dia = 6.500 min Pitch dia = 5.850 − 5.945 Minor dia = 5.417 − 5.607
Designation of Multiple Start Threads: When a thread is required with a multiple start, it is designated by specifying sequentially: M for metric thread, nominal diameter size, × L for lead, lead value, dash, P for pitch, pitch value, dash, tolerance class, parenthesis, script number of starts, and the word starts, close parenthesis. Examples: M16 × L4 − P2 − 4h6h (TWO STARTS) M14 × L6 − P2 − 6H (THREE STARTS) Designation of Coated or Plated Threads: In designating coated or plated M threads the tolerance class should be specified as after coating or after plating. If no designation of after coating or after plating is specified, the tolerance class applies before coating or plating in accordance with ISO practice. After plating, the thread must not transgress the maximum material limits for the tolerance position H/h. Examples: M6 × 1 − 6h AFTER COATING or AFTER PLATING M6 × 1 − 6g AFTER COATING or AFTER PLATING Where the tolerance position G/g is insufficient relief for the application to hold the threads within product limits, the coating or plating allowance may be specified as the maximum and minimum limits of size for minor and pitch diameters of internal threads or major and pitch diameters for external threads before coating or plating. Example: Allowance on external thread M profile based on 0.010 mm minimum coating thickness. M6 × 1 − 4h6h − AFTER COATING BEFORE COATING The MJ screw thread is intended for aerospace metric threaded parts and for other highly stressed applications requiring high temperature or high fatigue strength, or for “no allow ance” applications. The MJ profile thread is a hard metric version similar to the UNJ inch standards, ANSI/ASME B1.15 and MIL-S-8879. The MJ profile thread has a 0.15011 P to 0.180424 P controlled root radius in the external thread and the internal thread minor diam eter truncated to accommodate the external thread maximum root radius. First issued in 1978, the American National Standard ANSI/ASME B1.21M-1997 (R2018) establishes the basic triangular profile for the MJ form of thread; gives a system of designations; lists the standard series of diameter-pitch combinations for diameters from 1.6 to 200 mm; and specifies limiting dimensions and tolerances. Changes included in the 1997 revision are the addition of tolerance class 4G6G and 4G5G/4g6g comparable to ANSI/ ASME B1.15 (UNJ thread); the addition of tolerance class 6H/6g comparable to ANSI/ ASME B1.13M; and changes in the rounding proceedure as set forth in ANSI/ASME B1.30. Diameter-Pitch Combinations.— This Standard includes a selected series of diameter- pitch combinations of threads taken from International Standard ISO 261 plus some addi tional sizes in the constant pitch series. These are given in Table 1. It also includes the standard series of diameter-pitch combinations for aerospace screws, bolts, nuts, and fluid system fittings as shown in Table 2. Major dia = 5.780 − 5.940 Pitch dia = 5.239 − 5.290 Metric Screw Threads—MJ Profile
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