Threads and Threading - Sportpilot.info

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1846 ALTERNATIVE CENTRALIZING ACME SCREW THREADS
One-half
major dia.
allowance
Internal Thread
(Nut)
Basic thickness of thread, P/2
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0.15P
Machinery's Handbook 27th Edition
Max major dia. of nut
Min major dia. of nut
Nominal (basic) major dia. (D)
Max major dia. of screw
Min major dia. of screw
Min depth of
engagement
h
Max pitch dia.
of screw
Min pitch dia.
of screw
Basic pitch dia.
1/2 Pitch dia. allowance
Max minor dia. of nut
Min minor dia. of nut
Basic minor dia.
Max minor dia. of screw
Min minor dia. of screw
P′
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External Thread
(Screw)
Min minor dia. of screw
Min pitch dia. of nut
Limits of Size, Allowances, Tolerances, and Crest Clearances for
American National Standard Stub Acme Threads
One-half
major dia.
allowance
Stub Acme Thread Designations.—The method of designation for Standard Stub Acme
threads is illustrated in the following examples: 0.500-20 Stub Acme indicates a 1 ⁄ 2-inch
major diameter, 20 threads per inch, right hand, single thread, Standard Stub Acme thread.
The designation 0.500-20 Stub Acme-LH indicates the same thread except that it is left
hand.
Alternative Stub Acme Threads.—Since one Stub Acme thread form may not meet the
requirements of all applications, basic data for two of the other commonly used forms are
included in the appendix of the American Standard for Stub Acme Threads. These socalled
Modified Form 1 and Modified Form 2 threads utilize the same tolerances and
allowances as Standard Stub Acme threads and have the same major diameter and basic
thread thickness at the pitchline (0.5P). The basic height of Form 1 threads, h, is 0.375P;
for Form 2 it is 0.250P. The basic width of flat at the crest of the internal thread is 0.4030P
for Form 1 and 0.4353P for Form 2.
The pitch diameter and minor diameter for Form 1 threads will be smaller than similar
values for the Standard Stub Acme Form and for Form 2 they will be larger owing to the
differences in basic thread height h. Therefore, in calculating the dimensions of Form 1 and
Form 2 threads using Formulas 1 through 12 in Table 14a, it is only necessary to substitute
the following values in applying the formulas: For Form 1, D 2 = D − 0.375P, D 1 = D −
0.75P; for Form 2, D 2 = D − 0.25P, D 1 = D − 0.5P.
Thread Designation: These threads are designated in the same manner as Standard Stub
Acme threads except for the insertion of either M1 or M2 after “Acme.” Thus, 0.500-20
Stub Acme M1 for a Form 1 thread; and 0.500-20 Stub Acme M2 for a Form 2 thread.
Former 60-Degree Stub Thread.—Former American Standard B1.3-1941 included a
60-degree stub thread for use where design or operating conditions could be better satisfied
by the use of this thread, or other modified threads, than by Acme threads. Data for 60-
Degree Stub thread form are given in the accompanying diagram.
Copyright 2004, Industrial Press, Inc., New York, NY
0.15P