OnGuard Bulldog Series U-Locks. Features: Double Bolt Locking Mechanism provides added strength by locking the crossbar to the shackle on two sides Features 13mm ultra hardened steel shackles for maximum cut resistance Dust covers and vinyl coating protects the crossbar, shackle and cylinder from damage Includes multi-size/multi-position mounting bracket, (5) keys (1 with micro-light and 4 regular keys), plus OnGuard's anti-theft protection plan LS: long shackle model for added convenience ATB: slightly wider shackle to fit around extra-fat tires STD: sized to fit most any bike on the market LM: Lean and Mean is the lightest full size U-lock on the market DT: includes four foot cable with lock loops on each end Combo: features user resettable 4-digit combination Mini: short shackle model fits in a back pocket Medium: slightly longer than Mini Specs: Model:Bulldog STD LM Width X Length:4.5" x 9" Crossbar:13mm