136224 ⎘
Mine roof supports for step- by- step movement, e.g. in combination with provisions for shifting of conveyors, mining machines, or guides therefor; Structural features of the supporting construction, e.g. linking members between adjacent frames or sets of props; Means for counteracting lateral sliding on inclined floor; Special mine caps or special tops of pit-props for permitting step-by-step movement Pivoted cantilever extensions therefor