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