Single Cylinder Mortise Locks: An entry set which is operated by key on the exterior and a thumb-turn on the interior. A single cylinder lock is most frequently used in residential locations. Double Cylinder Mortise Locks: An entry set which is operated by key on both the exterior and interior sides of the lock. Double cylinder locks are most frequently used on glass doors, or doors that are not far from an easily broken window or sidelight. Dummy Set Mortise Locks: Dummy handle sets are almost always used in conjunction with a matching single or double cylinder handleset. These are intended for use on the inactive door in a set of double doors.
A mortise style lock is the most secure form of an entry set. The reason? A special cut in the door allows a longer and thicker mortise to slide into the pocket in the door itself, providing superior protection. These types of locks require special door preparation, so if your door isn’t currently cut to fit this kind of lock, you (or a professional installer) will need to use a deep lock mortiser to cut into the door so the lock fits properly. Take note that not all mortise locks have the same dimensions. So prior to any door alteration, take careful measurements. Read Entire Article