Lock casing

A lock casing (1) having a bolt (8) that comprises a bolt body (8b) inside the lock casing and a bolt end (8a) that in its locking position protrudes out of a bolt opening (2a) in the lock casing's front plate (2), at least one operating axis (3), transmission means (4, 5, 7, 9) for moving the bolt and means (6, 7, 7b, 9) for deadlocking the bolt. There is a preferably plate-like protective piece between the lock casing (1) and the bolt body (8b), and it is arranged to prevent a tool or similar item to be inserted through the bolt opening (2a) into the lock casing (1) in a position that affects the deadlocking means (6, 7, 7b, 9). The protective piece (10) is supported on the bolt (8) so that it moves together with the bolt (8).