The invention relates to mine working apparatus including a sprag plate 21. The sprag plate 21 is included in a sprag unit 20 that can be reciprocated in the fore-and-aft direction of the canopy and the sprag unit 20 includes a sprag slide 22 and a link system 43 and 61 that can be reciprocated in the fore-and-aft sense relatively to each other. There is a range of lost motion between the slide 22 and the link system and the means 48 for moving the sprag unit between the position in which the sprag plate 21 is operative and the position in which the sprag plate 21 is inoperative also moves the sprag slide and the link system relatively to each other through their range of lost motion and this relative movement swings the sprag plate 21 between a generally upright, operative, position and a generally horizontal, retracted, position.