Arri standard is a lens mount developed by Arri for use with both 16 mm and 35 mm movie cameras. Lenses are distinguished by a tab inside an outer ring. Because of the weak seating strength and ability of the aluminum mount to gradually become poorly seated, the stainless steel Arri bayonet mount superseded the Arri standard mount in 1965, debuting on the 16BL. However, cameras with the bayonet mount are also able to accommodate Arri standard lenses due to both mounts having the same flange focal distance and diameter. Unfortunately, cameras with Arri standard mounts are unable to fit lenses with Arri bayonet mounts, due to the bayonet mount's locking mechanism.
Flange focal distance: 52.00 mm
Diameter: 41.00 mm
Cameras: (all are Arri models)
35 mm: 1, 2, 2A, 2B, 2C
16 mm: S, SB (two turrets), ST, ST/B (two turrets), M
Material from http://en.wikipedia.org/wiki/Arri_standard