Founded in 1912, PMC Industries has a long history in the pipe and tube market, which is outside the scope of this website, but they also manufactured machinery and tooling related to thread cutting machinery. In more recent years, they merged with Belgian lathe maker M.P. Colinet to form a new company, PMC-Colinet.
One product they are particularly known for is the PMC SquareMaster, a reference vertical surface for use on a granite surface plate. The vertical surface, which is made of granite within a metallic housing, is flat and perpendicular to the surface plate within 50 millionths of an inch over 18 inches. This device was developed in the mid-1960s and was granted a 1969 patent.