Arri bayonet is a lens mount developed by Arri for use with both 16 mm and 35 mm movie camera lenses. Lenses of this type are distinguished by "outer wings" which both control aperture and bayonet alignment, and are placed in the mount while two pressure tabs are simultaneously depressed at the side of the lens mount on the camera. These tabs provide a relatively strong locking mechanism which allows for higher quality lens seating than offered by the Arri standard mount. Debuting in 1965 with the 16BL, the Arri bayonet mount superseded the Arri standard mount, but cameras with the bayonet mount were also able to accommodate Arri standard lenses due to both mounts having the same flange focal distance and diameter. However, cameras with Arri standard mounts were unable to fit lenses with Arri bayonet mounts, due to the locking mechanism. The bayonet mount began to be superseded around 1980 by the Arri PL mount, which has since become an overwhelmingly predominant mount for most modern cameras, along with Panavision and their PV mount.
Flange focal distance: 52.00 mm
Diameter: 41.00 mm
Cameras: (all are Arri models)
35 mm: Arriflex 35IIC (later models), Arriflex 35BL1, Arriflex 35BL2, 35BL3 (early models), and Arriflex 35III (early models);
16 mm: SB (only one turret), ST/B (only one turret), M/B, 16BL, Arriflex 16SR, and Arriflex 16SR2 (early models).
Material from http://en.wikipedia.org/wiki/Arri_bayonet