A mat (1) or other type of covering material is given a number of cross shaped cuts. The plate (4) to which the material is to be applied has a number of mushroom bolts, or bolts of T-shaped cross section which are attached to the plate with the heads a short distance from the plate. The positions of the cross cuts in the material correspond with the positions of the bolts in the plate. The material is placed on the plate so that the heads of the bolts can pass through the openings formed by folding back the sections of the cuts. The folded back sections are then pushed back under the bolt heads
