Mine roof supports

A mine roof support having a roof engaging cover and a forepole, in which the cover is formed by a leading and trailing part with the former recipropable within a continuous range of movement relatively to the latter so that the overall length of the cover may be varied, the forepole is associated with the leading part, fluid operated piston means are connected between the forepole and the trailing part and the stroke of the piston means is such that the forepole may be reciprocated in the fore-and-aft direction relatively to the trailing part through a continuous range of which a section lies forwardly of the range of movement of the leading part relatively to the trailing part, abutment surfaces provided by the leading part and the forepole co-operate when the leading part is retracted and the forepole reaches the forward end at the forwardly lying section so that further forward movement of the forepole results in corresponding forward movement of the leading part, and further abutment surfaces provided by the leading part and the forepole co-operate when the leading part is extended relatively to the trailing part and the forepole reaches the rearward end of the forwardly lying section so that further rearward movement of the forepole results in corresponding rearward movement of the leading part.