The Yale PM322 3 Lever Deadlock Polished Brass is used for internal doors which require some additional security, such as cupboards, studies and master bedrooms.  It can be used separately with a pull handle or in combination with a handle on a tubular latch. One case sizes is available; 64mm with a 45mm backset. 3 Lever Security versus 5 Lever The PM322 lock is a 3 lever lock which means it has 150 different key options.  It is also not as sturdy as a 5 lever insurance rated lock.  Hence it is best used for low level security doors, if a higher level of security is ...