American National Standard Stub Acme Threads are defined in ASME/ANSI
B1.8 and are for 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 Stub ACME screw thread form can be applied to either Genrral or Centrializing ACME screw threads.
The Major and Minor Diameter allowances for Stub Acme threads
are the same as those given for General Purpose or Centrializing Acme screw threads. Pitch
Diameter allowances for Stub Acme threads are the same as for Class
2G General Purpose or Centrializing Acme Screw Threads. Stub Acme Threads have a preferred series of diameters and pitches
which happens to be the same as General Purpose or Centrializing Acme Screw 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.
Complicating the world of ACME further, 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. Using the modified form does not eliminate the requirement for identifying the class-of-fit.
Modified Form 1, (M1) - The pitch and minor
diameters will be smaller than similar values for the standard form.
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)
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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This data is provided for general information only. The intention
is to provide accurate information; regardless; errors may exist
in the supplied information. If accuracy is critical, base your
final decisions on the data provided in the root document: ANSI/ASME
B1.8; which is a copyrighted document. To purchase a copy visit
an Authorized Reseller.
Original Posting: 7/14/2009
Last Revision: 5/15/2020
Error corrections in, or comments about, the above data can be sent to: firstname.lastname@example.org