{TAIL ~ An inner housing} defines a cylindrical outer wall and, together with {HEAD ~ the substantially cylindrical inner wall}, forms a substantially cylindrical ring gap 
{ TAIL ~ An inner housing } defines a cylindrical outer wall and , together with { HEAD ~ the substantially cylindrical inner wall } , forms a substantially cylindrical ring gap
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH