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