However, the term, USS, continues to be used occasionally today to describe inch based threaded fasteners with a coarse thread pitch and inch based washers that are a little bit larger than the corresponding SAE washer.
The Unified Thread Standard uses the term UNC (Unified Coarse) to describe a fastener that previously would have been designated USS and UNF (Unified Fine) to describe a fastener that would have previously been designated SAE.
[1] William Sellers originally developed the USS thread, and set forth many of its details in his paper, "A System of Screw Threads and Nuts", presented in April 1864 to the Franklin Institute.
In 1898, the standard for metric threaded fasteners was established.
[5] The metric standard used the same thread geometry as the USS standard but differed in that the dimensions and pitch were based on metric units.