I want to make a small go kart and im have trouble with axles?
The set screw in the axle hangar fixes the bearing's inner race to the axle shaft so it won't slide from side to side on the axle shaft. The bearing is constructed so that it's parts can handle some side loading without coming apart, in other words the bearing's inner race and outer race are allowed to rotate freely with respect to each other, but any side loads from going around a corner are transmitted from the axle to the bearing holder and frame. So side loads on the axle transfer to the inner race (due to set screw), to ball bearings, to outer race. Outer race is solidly attached to bearing holder, bearing holder is solidly bolted to frame.