Threads and Threading - Sportpilot.info

1804 METRIC SCREW THREADS MJ PROFILE
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
Machinery's Handbook 27th Edition
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
Major dia = 5.780 − 5.940
Pitch dia = 5.239 − 5.290
Metric Screw Threads—MJ Profile
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
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 allowance”
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 0.15011P to
0.180424P controlled root radius in the external thread and the internal thread minor diameter
truncated to accommodate the external thread maximum root radius.
First issued in 1978, the American National Standard ANSI/ASME B1.21M-1997 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 B1.30M.
Diameter-Pitch Combinations.—This Standard includes a selected series of diameterpitch
combinations of threads taken from International Standard ISO 261 plus some additional
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.
Copyright 2004, Industrial Press, Inc., New York, NY