Stainless steel case with double-wall construction and nickel-plated steel shackle. 3-number dialing. Permanently lubricated. Dial cannot be turned when shackle is under tension, safe-guarding combination. Key-controlled model has master-key mechanism - authorized person has access to all lockers. (Order Control Keys separately). Installation record maintained at factory, permitting extension of system under same key. Combination padlock does not have master-key control. Minimum order is 15 locks. If you need your new key controlled locks to work with an existing lock system, please specify your current control key number on your order.