Round pin board large arrows left and right ears top beam accessories: metal roof beam horizontal wedge fitting large arrow left and right ears stalls circle round pin board DJB metal hinged roof beams suitable for all types of metal with a hinged roof pillar (single or friction pillars) consisting of metal stents, for horizontal and gently inclined coal mining face roof supporting use. This can be achieved due to the cantilever roof beams supporting, the coal pillar between the wall and there is no support larger space for the realization of the general mechanization of coal mining conditions. The product is only suitable for blasting mining face, but also atmining face roof support of the necessary equipment.