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