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.

The first lenses were plain stop-down design, but many manufacturers extended the M42 lens mount to provide extra features.

A further development followed with "auto" lenses, which have a pin in the mount which closes the aperture against a spring to the chosen setting when it is pushed.

The means of doing this was not standardised, Praktica's method was to use an electrical connection which transmitted a variable resistance value to the camera's metering circuit.

Asahi Pentax developed an additional lever on the lens which operated a variable resistor in the camera mount.

These cameras retained the facility of closing the aperture with finger pressure on the release button so that the image could be framed and focused normally with the lens wide open.

As the shutter button was depressed the lens would firstly be stopped down to the selected aperture, then the meter would be switched on and a reading taken.

While this method did not offer the same sensitivity advantage of true open-aperture metering, it was much more versatile as it did not require specially-equipped proprietary lenses.

Compatibility problems have been experienced when mounting lenses with aperture transmission levers (e.g., SMC Takumars) on older bodies such as Zenit-E or Mamiya DTL.

The aperture lug or a pin can interlock with the slotted screwheads affixing the mount, which then impedes lens removal.

M42 mount cameras fell out of general production during the late 1970s and early 1980s, with the exception of the Russian Zenit range.

M42 adapters work best on bodies with a flange depth less than or equal to the M42's flange depth, which includes the popular Canon EF-mount, the Pentax K-mount, the Minolta/Konica Minolta/Sony A-mount, the Sony E-mount, the Samsung NX-mount, the Fujifilm X-mount and the Four Thirds System including the Micro Four Thirds system.

Alternatively, an adapter with an optical element can be used to retain the original focus range of the lens, at the expense of some image quality.

Mounting an M42 lens on a digital SLR with a sensor smaller than 35 mm film results in FOV crop.