The Pro tactic frame lock features a 8.5mm steel shackle. With an extra wide aperture - 2.48" wide and 4.25" height clearance from shackle to top of lock body - the 4960 will accommodate a variety of tire/wheel sizes. The case, 8.5mm shackle, and supporting elements of the locking mechanism are all made of special Temper hardened steel. The locking mechanism is in the lock body for an easy connection to the optional accessory chains and cables. The 4960 can be mounted to the bike using either the cantilever brake mount option or the span band lh adapter for bikes without screw/bolt sockets.