The internal diameter of {HEAD ~ the tube section} 20 is equal to {TAIL ~ the internal diameter} of the adjacent parts of pipes 10 and 12 
The internal diameter of { HEAD ~ the tube section } 20 is equal to { TAIL ~ the internal diameter } of the adjacent parts of pipes 10 and 12
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH