Stainless steel spreader support plates mount on either side of the mast, to tighten up your spreader bar from wobbling and play in the existing mast slot. (8) 3/16” Stainless steel rivets included (Use a .192” to .194” drill for mounting - #11 or #10 Drill bits). Easy notched cutout allows for fine tune filing, to get a TIGHT fit on the spreader bar. Slid on the bar while mounted in the mast, and drill and rivet to the mast. The gauge of the plate allows it to conform nicely to the camber of the mast, for a nice flush mount. Once mounted on the mast, file the inboard ends of the spreaders to accommodate the added thickness from the plates. Comes as a set of (2).