This purchase is for a pair fo frame sliders. The slider pucks are made of UHMW-PE (ultra high molecular weight polyethylene), a tough plastic with good strength, wear resistance and dimensional stability. The slider pucks are made of UHMW-PE (ultra high molecular weight polyethylene), a tough plastic with good strength, wear resistance and dimensional stability. The sliders are made of two independent pieces: the aluminum bases and the pucks. This design allow the easy and inexpensive replacement of the slider pucks. The bolts are made of highest grade commercially available 12.9(177,000 psi in tensile strength). The brackets are made and machined from solid steel about x2 stronger than aluminum brackets(6061). Rest assured that you are getting the best material commercially available.