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Microscope Objective Screw Threads ANSI/ASME B1.11

Microscope Objective Screw Threads ANSI/ASME B1.11

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 websites have embedded the old documents and thus the erroneous data is lingering in cyberspace.

The AMO screw thread is only one size of thread. It is specified in multiple standards 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.

Initial Posting: 10/12/2009
Last Revision: 4/7/2010
If you have comments or questions related to this information contact Wayne at:gageguy@gagecrib.com

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