One side wall of {HEAD ~ the housing} defines {TAIL ~ an opening} through which the tubing reel may be slidably removed 
One side wall of { HEAD ~ the housing } defines { TAIL ~ an opening } through which the tubing reel may be slidably removed
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH