This purchase is for a pair of engine case covers, designed to help protect your bike in the event of a low-side. The covers 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 bolts are made of highest grade commercially available 12.9(177,000 psi in tensile strength). Rest assured that you are getting the best material commercially available.