A cylinder nightlatch should not be the main lock chosen for security on an external door. It is not too difficult to interfere with, and is less secure than a deadbolt cylinder nightlatch. It is more suitable for use on a back or side door, in conjunction with top and bottom bolts. It is fitted to the inside of the door with screws.
If you are replacing an existing nightlatch, make sure it is the same dimensions as the previous one and the holes for the key are in the same positions. This type of latch is operated by a key on the outside and a handle from the inside of the door. The deadbolt facility stops someone forcing the lock when the door is closed and the key turned from either the outside or inside of the property.
Use the body of the lock as a template to mark the positions of the fixing screws. By holding the lock against the door, mark the position of the keyhole with a bradawl. Drill a hole for the keyhole, and, by holding a spare block of wood on the other side of the door, you will stop any splintering of wood as the drill bit passes through. Use a padsaw to cut out the shape for the keyhole to fit.
Screw the lock into position and check that it operates properly. Push the door until almost closed and mark on the jamb the position of the striking plate. Open the door again and chisel out a recess for the body of the striking plate. Then screw the striking plate into position.
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