The Spidertrax Chromoly Full Floater End Cup Kit makes it easy to build your Spider 9 Housing into a competition grade full floating rear axle. Each cup is manufactured out of 4130 chromoly steel, and is designed to press fit onto a Spider 9 housing with 4″ (101.6mm) OD tube while accepting Spidertrax Pro Series Unit Bearings (mounting hardware included). In addition, each cup has an integrated caliper mounting tab to easily install a bolt-on Spidertrax Caliper Mount Kit. Pro Series Unit Bearings and Caliper Mount Kits are sold separately. ???????