Mortice lock /Yale/yale_com_eg/Images/egypt%20internal%20mort.jpg Mortice locks can be found in a number of variations. For internal doors a classic sash lock or dead bolt is recommended. A sash lock is operated by a lever handle and a cylinder. A deadlock is operated by cylinder only. For external doors a security sash lock or dead bolt should be chosen. In order to increase the level of security a high security cylinder is recommended.