The outlet shell which defines the outlet chamber is adapted to engage {HEAD ~ the inside} of {TAIL ~ the pair} of shells which form the catalyst chamber 
The outlet shell which defines the outlet chamber is adapted to engage { HEAD ~ the inside } of { TAIL ~ the pair } of shells which form the catalyst chamber
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH