Stub Acme 29 Degree Threads

American National Standard Stub Acme Threads:- This American National Standard ASME/ANSI B1.8-1988 (R2001) provides a Stub Acme screw thread for those unusual applications where, due to mechanical or metallurgical considerations, a coarsepitch thread of shallow depth is required. The fit of Stub Acme threads corresponds to the Class 2G General Purpose Acme thread in American National Standard ANSI B1.5-1988. For a fit having less backlash, the tolerances and allowances for Classes 3G or 4G General Purpose Acme threads may be used.

Thread Form : The thread form and basic formulas for Stub Acme threads are given above and the basic dimensions in the below Table .

Allowances and Tolerances

The major and minor diameter allowances for Stub Acme threads are the same as those given for General Purpose Acme threads on page 1825. Pitch diameter allowances for Stub Acme threads are the same as for Class 2G General Purpose Acme threads. Pitch diameter tolerances for Stub Acme threads are the same as for Class 2G General Purpose Acme threads.

Thread Series

A preferred series of diameters and pitches for General Purpose Acme threads is recommended for Stub Acme threads.

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, D2 = D - 0.375P, D1 = D - 0.75P; for Form 2, D2 = D - 0.25P, D1 = 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.

Limiting Dimensions

Limiting dimensions of American Standard Stub Acme threads may be determined by using the formulas given in below Table. The diagram below shows the limits of size for Stub Acme threads.