This purchase is for a pair of frame sliders for the models above. The sliders 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. The bolts are made of highest grade commercially available 12.9(177,000 psi in tensile strength). The brackets are made of aircraft grade aluminum 6061-T6 The cross bolt is made of 304 stainless steel powder coated in black. The aluminum spacers are made of 6061-T6. Rest assured that you are getting the best material commercially available.