The Kryptonite KryptoFlex 1218 Combo bike lock is a braided steel cable 12mm thick with a protective vinyl cover that provides greater resistance to cutting attacks. The opening and closing system is a four-digit combination lock, no keys are needed. The lock head at the ends of the cable have been reinforced to provide additional strength. The manufacturer gives it a security rating of 2 of 10, recommended for use as a secondary deterrent. MORE INFORMATION: How to choose the best lock to protect your bike?