If you dread keys, the Shackleton is the ticket. You can program in your own four-digit code for easy opening each time. Silicone over mold and quick, push-button release shackle will protect your bike in most environments. Security rating: 5, 12mm hardened steel shackle, durable 4 DIGIT customizable combination, attack resistant, heavy-duty combination wheels, 3. 75″ x 6. 7″