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