6061 Billet Aluminum, completely CNC machined. Uses the larger clutch bell bearings from our HD Baja Clutch system, bigger than the stock Losi bearings but use your stock clutch bell. Better bearing life and heat dissipation. Radial Heat sink WILL remove heat from bell and bearings. The carrier is also vented so gasses are not trapped and forced into your crank bearings. Support ribs for bearings are hidden inside heat sinks to add extra support to your bearing, gear and bell. This is a VERY strong unit but still very light weight.