Jaw crushers for crushing rock and other minerals conventionally comprise a fixed jaw and a movable jaw which define a crushing chamber of a cross section which narrows from top to bottom. The movable jaw is pivotally supported at its upper end so that the lower end of the jaw can be driven in a swinging motion towards and away from the lower end of the fixed jaw. Material to be crushed is introduced into the upper end of the crushing chamber formed between the two jaws and is crushed between the two jaws by the swinging movement of the movable jaw as the material moves downwardly through the chamber, the crushed material being discharged from the chamber at its lower end. The crushing surfaces of the two jaws are subject to substantial wear and are conventionally formed by replaceable faces which are fixed to the body of the jaw by being bolted and keyed. Usually, to facilitate breakage of the rock the surface of each replaceable jaw face is corrugated, with the axes of the corrugations extending in a vertical direction and normally each jaw carries two separate jaw faces, namely an upper face and lower face.