Abstract: Backrest or back modules for stadium seating molded of plastic material are securely fastened along lateral edges to barlike support uprights by clips. Edges of adjacent backrest modules are inserted into upper and lower lips on the back supports; the opposed edges of the backrest modules are clamped by a single clip and abut a center stiffening rib on the supports. The clip has opposed horizontal reinforcing ribs which engage and clamp the brackrest module edges. The reinforcing ribs of the clip are chamfered so that as the clip is installed, the adjacent backrest module edges are drawn in or cammed snuggly against the center stiffening rib. Additional pressure applied by the fastener causes the reinforcing ribs of the clip to impress into the edges of the backrest modules causing surface cold-flow of the plastic material, thus eliminating both vertical and lateral movement.