ABUS Granit X Plus 54 D-Lock & Bracket As secure as Fort Knox Strong 13 mm square patented parabolic shackle offers a very high degree of protection against extreme physical attack. How it works: Fixing your bicycle at a solid object (e.g. lamp post, sign, fence) Technology: With ABUS patented 'power cell' technology which double locks the shackle into the lock body & an ABUS X Plus disc cylinder for the highest protection against intelligent opening methods, the ABUS 54 is As secure as Fort Knox