{HEAD ~ The upper end} is optionally secured to {TAIL ~ the open lower end} of the T shaped two piece housing 
is optionally secured to
{ HEAD ~ The upper end } is optionally secured to { TAIL ~ the open lower end } of the T shaped two piece housing
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH