Rim lock

A rim lock is a locking device that attaches to the surface of a door.

The original type of lock used in England and Ireland. It is of a basic design originally of a very stiff lever and a bolt with wards being the block. As wards were outdated in the centre of the key, it became normal for them to be placed on the sides of the bit. Although today these are still produced they are mostly for internal doors and are not used for high security. Older locks could be as large as 40 cm by 25 cm. Most rimlocks used today on exterior doors in the British Isles are nightlatches.

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Wikipedia