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