M42 mount

The M42 SLR lens mount is the most popular screw thread mounting standard for attaching lenses to 35 mm SLR film cameras, primarily single-lens reflex models. It is more accurately known as the M42 × 1 mm standard, which means that it is a metric screw thread of 42 mm diameter and 1 mm thread pitch.

It was first used by the East German brands VEB Zeiss Ikon in the Contax S of 1949, and KW in the Praktica of the same year. VEB Zeiss Ikon and KW were merged into the Pentacon brand in 1959, along with several other East German camera makers.

M42 SLR thread mount cameras first became well known under the Praktica brand, and thus the M42 SLR mount is known as the Praktica thread mount. Since there were no proprietary elements to the M42 mount, many other manufacturers used it; this has led to it being called the Universal thread mount or Universal screw mount by many. The M42 SLR mount was also used by Pentax; thus, it is also commonly known as the Pentax thread mount, despite the fact that Pentax did not invented it.