ACME Screw Threads

American National Standard Stub Acme Threads can be found is ASME/ANSI B1.8 and are for those atypical applications where, due to mechanical or metallurgical considerations, a coarse-pitch thread of shallow depth (thin wall) is necessary. The fit of Stub Acme threads corresponds to the Class 2G General Purpose Acme Thread found in ASME/ANSI B1.5. For a fit having minimal backlash, the tolerances and allowances for classes 3G or 4G General Purpose Acme Threads may be used.

The Major and Minor Diameter allowances for Stub Acme threads are the same as those given for General Purpose Acme threads. 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. Stub Acme Threads have a preferred series of diameters and pitches which happens to be the same as General Purpose Acme Threads.

The proper method of designation for Standard Stub Acme threads is illustrated in the following examples: 0.500"-20 Stub Acme-2G indicates that the thread has a ½" major diameter, 20 threads per inch, class 2G, right hand, single thread, Standard Stub Acme thread. This Designation stays the same with Left Handed Threads except you add LH behind the description, for example: 0.500"-20 Stub Acme-2G LH.

Recognizing that the Standard Stub Acme does not always provide an accepted thread for all applications basic data for two other frequently used forms have been tabulated. These are designated MODIFIED Forms 1 and 2. You are strongly urged to ALWAYS use the Standard Stub Acme form in preference to the Modified form where it is realistic. For Modified Form 1, (M1) - the pitch and minor diameters will be smaller than similar values for the standard form. For Modified 2, (M2) - the pitch and minor diameters will be larger than values for the standard form. Thread designation is the same as the Standard Stub Acme except that you add the M1 or M2 after the Class or hand in case of a LH thread (i.e. 0.500"-20 Stub Acme-2G M1 or 0.500"-20 Stub Acme-2G LH M1)

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For more information click the links below:(links not active yet) 
" Stub Acme Thread Profile
" Stub Acme Thread Data
" Stub Acme Modified (M1,M2) Thread Profile
" Stub Acme Modified (M1,M2) Thread Data

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