Built ground up for Ultra4 rock racers, the Spidertrax Ultimate Unit Bearing is truly the reinvention of the unit bearing itself. Genuine Timken bearings, full chromoly heat treated construction, and a fully integrated drive slug makes the Ultimate Unit Bearing the only racing unit bearing of its kind. The Ultimate Unit Bearing, the last bearing youll ever need. This Ultimate Unit Bearing uses (?”, 15.9mm)-18 studs on a 6 on (6½”, 165.1mm) bolt circle, designed specifically for Spidertrax 40 splined axle shafts. Overview Durable Full chromoly heat treated construction, genuine Timken bearings, built right at our shop in Colorado. Simply the last bearing youll ever need. Compact With a span of just 2.125″ (54mm) from flange to wheel mount, the Spidertrax Ultimate Unit Bearing is the perfect fit for an Ultra4 solid or IFS axle. Innovative Less parts means less headache. Weve eliminated the need for a drive slug, while adding a 4.235″ (107.6mm) hub register for wheel centering & strength. Secure Spindle nuts are not only thread locked into place, we also use a keyed lock ring. This means never having to worry about loosening spindle nuts.