12mm six-sided, chain links made of 3T HARDENED MANGANESE STEEL for maximum strength. Durable, protective nylon cover with hook-n-loop fasteners to hold in place. Includes Evolution series 4 Disc Lock with 14mm MAX-PERFORMANCE STEEL SHACKLE. Patented*, oval hardened STEEL CROSSBAR for extra security. Hardened DOUBLE DEADBOLT locking for extensive holding power. HIGH SECURITY DISC-STYLE CYLINDER with reinforced anti-drill, anti-pull protection system. SLIDING DUSTCOVER protects and extends cylinder life. 3 STAINLESS STEEL KEYS - one lighted with high intensity bulb and replaceable battery. Key Safe Program. Patent D564339