Bike-Guard's Rocklink 1600 is a 4 foot long chain lock with 10mm-thick hardened-steel links with narrow inner diameters to resist prying attacks. And, it includes Bike-Guard's double-locking, solid-steel Power Chamber lock. It boasts a 16mm-thick shackle and an anti-drill, anti-pull/pry reinforced lock cylinder. For weather resistance and to protect your bike's finish, the chain has a ballistic nylon cover and the lock is plastic coated. Plus, the Rocklink comes with Bike-Guard's $2,500 anti-theft protection policy.