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