The extension has an inner diameter less than {HEAD ~ the inner diameter} of the remainder of {TAIL ~ the annular protrusion} 
The extension has an inner diameter less than { HEAD ~ the inner diameter } of the remainder of { TAIL ~ the annular protrusion }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL