Each of {HEAD ~ the sides} has an empty space frame by {TAIL ~ outer edges} of the housing side 
Each of { HEAD ~ the sides } has an empty space frame by { TAIL ~ outer edges } of the housing side
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH