The
M42 lens mount is a
screw thread mounting standard for attaching lenses to
35 mm 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 in
Zeiss'
Contax S of 1949; this
East German branch of Zeiss also sold cameras under the
Pentacon name; after merger with other East German photographic manufacturers, the name
Praktica was used. M42 thread mount cameras first became well known under the Praktica brand, and thus the M42 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 mount was popularized in the
United States by
Pentax; thus, it is also known as the
Pentax thread mount, despite the fact that Pentax did not originate it.