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" OD tube while accepting a Spidertrax Ultimate Unit Bearing (mounting hardware included). In addition, each cup has an integrated caliper mounting tab to easily install the bolt-on Spidertrax Full Floating Caliper Mount Kit. The Ultimate Unit Bearing and Caliper Mount Kit is sold separately.