Pitbull Std Bicycle U LockPitbull series u locks provide superior protection for medium high crime areas, with many of the features of our Brute series and a slightly thinner shackle. Features X4P Quattro Bolt Locking Mechanism locks shackle at four points Z Cylinder is bump proof and resists pucking, pulling, and drilling TriRadius shackle creates more internal space for locking versatility Hefty 14mm thick hardened steel shackle resists cutting, prying, and jacking Rounded