The C-Series Line of MUL-T-LOCK Padlocks is designed to offer Patented High Security Key Control and Strong Physical Protection to Padlock Security. All C-Series Padlocks are made with a hardened steel body shell, and a hardened steel shackle. Drill and Pick Resistant Cylinder Bump Proof High Security Lock Cylinder. MUL-T-LOCK's Patented Interactive® Key Control System.