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