Rim locks were most of the time used earlier, before the more favorable mortise locks. They represent the tail end of an era when doors were locked by large, heavy boxed locks that fastened to the side of the doors. A rim lock is screwed to the door and aligned with its keeper that is on the frame of the door. These locks were also used on doors that were too thin to accept a mortise lock (one that fits inside the door). This rim lock is made of the heavy cast iron and probably dates to pre-1900. It is for a RIGHT-hand door.
The box that fastens to the door measures 4 1/4 inches wide and 3 1/4 inches vertically. There is a lock lever on the top to lock down the plunger. The box is 5/8 inch thick. The keeper is 7/8 inch wide, 3/4 inch thick and 3 1/4 inches long. The keyhole is 2 3/8 inches from the top of the box. A key is included.