{HEAD ~ A casing} is mounted to {TAIL ~ two respective outer peripheries} of the two end caps and accommodates the axle therein 
{ HEAD ~ A casing } is mounted to { TAIL ~ two respective outer peripheries } of the two end caps and accommodates the axle therein
HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH