The MC-12B replaces the MC-12A. The MC-12B is 31" long and works with the F4S and F-3 cameras using MD4 Motor Drive. Also works with the N70, N8008, N8008S, FM2, FE2, FE and FM, all with MD12 motor drive. The MC-12B will also work with the F5, N90 and N90S, but it requires pin adapter cord MC-25 (NT3045).