This CRL Window and Door Chain Lock has a heavy diecast key lockable base, with an 8" (203 mm) long chrome plated chain. Once this lock is mounted on either a window or door, the flexible chain allows for a small amount of opening for ventilation while providing extra security and preventing unexpected openings. Each lock set comes with an allen wrench for adjusting the chain length to suit the application. Mounting screws have a hex drive head. All locks are keyed alike, and are packed with one lock, chain, and two keys per package.