Locking device for a manhole

摘要

The device has a bolt (10) whose plate has notches supported on an inner side of base wall of a cavity (5) of a pad (1). Lateral surface of the cavity has two grooves (29), where width of each groove for passing a tang of a key bushing is lower than that of a notch as the grooves overhang the plate. The width difference permits a notch (14) to be inaccessible by a screwdriver in locked position of the pad with a frame.