This hub has an 8mm REX bore to match our 8mm REX shafting. The hex profile creates a positive drive that can handle heavy torque loads without concern of rounding out. The Sonic style hub is perfectly balanced for high-speed applications. The unique design conforms tightly around a shaft when tightened, without distorting the threaded holes on the goBILDA 16mm pattern. The outer profile is 32mm so that it can be run in a bearing to isolate radial loads, or even clamped around!