KEY-STOP

Essentially a metal pointer with the end bent downwards which is fixed under a standard handle and prevents operation in one direction only.

To release the stop the handle is unscrewed a little and the stop turned to one side.
 

This is an elliptical dome-shaped cap with two holes, one in the centre and one towards one end, which also is fixed under the handle.

It can be used to lock the key in the normal or either operated position, in the first case using the central hole and in the other the offset hole. To release the stop, the handle must be unscrewed completely and it is therefore only recommended for guarding keys which are used infrequently. In other cases, Handles, Key, Nos. 11 or 16 should be preferred.