Likewise, the seal could be made against the head of {TAIL ~ the plug} instead of on {HEAD ~ the face} of the tubesheet 
Likewise , the seal could be made against the head of { TAIL ~ the plug } instead of on { HEAD ~ the face } of the tubesheet
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH