7mm four-sided chain links made from 3T MANGANESE STEEL. Patent-pending END LINK DESIGN secures chain to hardened deadbolt eliminating critical vulnerability. Hardened DEADBOLT DEDSIGN provides extra holding power. HIGH SECURITY DISC-STYLE CYLINDER is pick and drill resistant. Includes 2 NEW ERGONOMIC "I" KEYS. Durable WEATHER-RESISTANT nylon sleeve prevents scratches. Key Safe Program