ALERT ALERT ALERT
The AMO screw thread is a 55° included angle screw thread. It
is the modified/truncated Whitworth screw thread form. Several published
pages, in hardcopy and on the Internet, identify this screw thread
as having a 60° included angle screw thread form. These published
pages are from respected screw thread gage makers whom have acknowledged
that the 60° designation was an error and have taken steps to
correct their published documents. Regardless, several web sites
have embedded the old documents and thus the erroneous data is lingering
The AMO screw thread is only one size of thread: 0.8000"-36 AMO. It is specified
in multiple standards (ASA B1.11; ISO 8038; DIN 58888; BS 7012-4.1) from various countries, but the thread details
are uniform from standard to standard. The Thread was codified in
1858 by the Royal Microscope Society. In 1958 an effort was made
to unify the screw threads among the inch-using countries which
eventuality lead to ASA B1.11 being ratified in 1958. Since that
time, in 1978 two changes were made to the standard, one of which
changing it to ANSI B1.11.
The ANSI B1.11 screw thread standard covers the single screw thread
size: 0.8000"-36 AMO. The standard lays out the screw thread
parameters and the parameters for screw thread gauging.
ANSI/ASME B1.11; Page 9; Appendix; Footnote: NOTE: Ring and plug gages made in accordance with the above dimensions are not suitable for checking British product, the rounded roots of which will not pass the flat crest truncations of the gages. However, British gages, which are made to check the full Whitworth form of thread, will accept American product.
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
B1.11; which is a copyrighted document. To purchase a copy visit
an Authorized Reseller.
Initial Posting: 10/12/2009
Last Revision: 7/31/2018
Error corrections in, or comments about, the above data can be sent