Threads and Threading - Sportpilot.info
Threads and Threading - Sportpilot.info
Threads and Threading - Sportpilot.info
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Machinery's H<strong>and</strong>book 27th Edition<br />
1790 METRIC SCREW THREADS M PROFILE<br />
Fig. 5. Metric Tolerance System for Screw <strong>Threads</strong><br />
Tolerance: The tolerance is defined by a series of numerical grades. Each grade provides<br />
numerical values for the various nominal sizes corresponding to the st<strong>and</strong>ard tolerance for<br />
that grade.<br />
In the schematic diagram the tolerance for the external thread is shown as negative. Thus<br />
the tolerance plus the fit define the lower deviation (ei). The tolerance for the mating internal<br />
thread is shown as positive. Thus the tolerance plus the fit defines the upper deviation<br />
(ES).<br />
Tolerance Grade: This is indicated by a number. The system provides for a series of tolerance<br />
grades for each of the four screw thread parameters: minor diameter, internal<br />
thread, D 1 ; major diameter, external thread, d; pitch diameter, internal thread, D 2 ; <strong>and</strong> pitch<br />
diameter, external thread, d 2. The tolerance grades for this St<strong>and</strong>ard ANSI B1.13M were<br />
selected from those given in ISO 965/1.<br />
Dimension Tolerance Grades Table<br />
D 1 4, 5, 6, 7, 8 Table 8<br />
d 4, 6, 8 Table 9<br />
D 2 4, 5, 6, 7, 8 Table 10<br />
d 2 3, 4, 5, 6, 7, 8, 9 Table 11<br />
Note: The underlined tolerance grades are used with normal length of thread engagement.<br />
Tolerance Position: This position is the allowance (fundamental deviation) <strong>and</strong> is indicated<br />
by a letter. A capital letter is used for internal threads <strong>and</strong> a lower case letter for external<br />
threads. The system provides a series of tolerance positions for internal <strong>and</strong> external<br />
threads. The underlined letters are used in this St<strong>and</strong>ard:<br />
Internal threads G, H Table 6<br />
External threads e, f, g, h Table 6<br />
Designations of Tolerance Grade, Tolerance Position, <strong>and</strong> Tolerance Class: The tolerance<br />
grade is given first followed by the tolerance position, thus: 4g or 5H. To designate the<br />
tolerance class the grade <strong>and</strong> position of the pitch diameter is shown first followed by that<br />
for the major diameter in the case of the external thread or that for the minor diameter in the<br />
case of the internal thread, thus 4g6g for an external thread <strong>and</strong> 5H6H for an internal<br />
thread. If the two grades <strong>and</strong> positions are identical, it is not necessary to repeat the symbols,<br />
thus 4g, alone, st<strong>and</strong>s for 4g4g <strong>and</strong> 5H, alone, st<strong>and</strong>s for 5H5H.<br />
Copyright 2004, Industrial Press, Inc., New York, NY