The yale pm552 5 lever mortice deadlocks offers a high level of security and are suitable for use on external timber doors the deadbolt on the lock is locked or unlocked by key from either side these deadlocks also have a 14mm anti saw deadbolt and are recommended for use on a front door in conjunction with a yale bs nightlatch a deadlock has a single deadbolt which is locked or unlocked and locked by means of a key from either side whereas a sashlock has both a deadbolt and a latch which is ope