Rim locks, as the name suggests, are surface locks commonly about 150mm by 100mm. Some types are smaller, while others are larger for decorative purposes.
As a security system, rim locks provide the most basic of security. A common make of rim lock will have no more than 15 to 20 different keys. They are usually fitted for aesthetic and decorative reasons and in recent years the number of rim locks available on the market has diminished. In general, a rim lock is held on by four screws and its keep by two screws; hence anyone with a simple screwdriver can remove the lock internally and open the door.
Household Door Locks
The origin of rim locks dates back to when many household doors were 25mm to 30mm thick and could not accommodate mortice locks. Today we typically use 35mm thick internal house doors and 45mm thick external doors along with 45mm thick doors, when the door has to be fire rated, as in flats and the door between your house and garage.
In the vast majority of cases a rim lock will be operated by a set of knobs which have either been made as a rim set, or can be fitted as a rim set. One knob will have a backing rose for the non-lock side of the door and one knob will have no rose for fitting to the lock side.