This purchase is for a pair of frame sliders for the above models. The slider pucks are made of UHMW-PE (ultra high molecular weight polyethylene), a tough plastic with good strength, wear resistance and dimensional stability. It is more dimensionally stable than Nylon and used in many industrial ball bearing and friction reducing applications. They can be inexpensively replaced in case of a low-side. The slider bases are made of 6061 T6 aluminum. The bolts are made of highest grade commercially available 12.9(177,000 psi in tensile strength). The brackets are made from solid steel plates. Rest assured that you are getting the best material commercially available.