Vehicle axles and structural components therefor, namely, hubs, hub assemblies, hub end units, bearings, bearing kits, spindles, spindle assemblies, u-bolts, hydraulic brakes, electric brakes, hangers, hanger kits, axle springs, spring shackles, hub studs, nuts, equalizer bars, tie plates, brake actuators, rotors, calipers, rubber torsion stubs and flex forks