Oxford Magnum U-Lock (170mm x 285mm) w/BracketThe Magnum is an ultra strong U lock. It boasts high security an independently approved 16mm shackle lock with hardened steel construction and has undergone rigorous testing achieving Sold Secure GOLD ART 4* SBSC and FG certification. The Magnum has a key replacement service. When you buy your Magnum simply note down the number which comes attached to the keys on a metal tag. Keep this in a safe place then in the event that you are unfortunate enough