OnGuard's Bulldog STD boasts an 13mm-thick hardened-steel shackle and OnGuard's stout X2 double-bolt lock that resists drilling, picking, bumping, and pulling for serious protection. And, thanks to the included mounting bracket you can bring the Bulldog along for every ride. This great U-lock also comes with five keys, including OnGuard's Microlight key, which has a built-in light. - All OnGuard locks feature integrated covers for protection from moisture and dirt. - OnGuard locks feature plastic, rubber, or vinyl at all contact points to protect your bike's finish. - Shackle Dimensions: 115mm x 230mm (W x H x Dia.) (4.53" x 9.06") x 13mm (0.51") D