The upper inside surface and the lower inside surface of {TAIL ~ the housing} define a group of {HEAD ~ slots} 
The upper inside surface and the lower inside surface of { TAIL ~ the housing } define a group of { HEAD ~ slots }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD