From Festipedia, hosted by the FR Heritage Group

A drawer-lock is a device for interlocking a train staff with other equipment.

The staff is placed in a drawer, with matching rings, and pushed close. The device may then do one of a number of things:

  • release an Annett key to release a set of points, especially at an intermediate siding.
  • release those points directly by some kind of mechanical linkage.
  • operate an electric switch, that might for example, release a starting signal.

The Drawer-lock has rings or other devices, so that only the staffs for that section may release that drawer-lock.

The drawer-lock cannot be opened to free the staff again, unless the Annett key, points, or electric switch are restored to normal. In the case of signals controlling section entry, a relay "remembers" the operation of the electric switch, so the drawer lock can be normalised immediately.