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