The tieback member of {HEAD ~ this invention} is used in {TAIL ~ the contingency} that the tieback threads in the casing hanger become damaged 
The tieback member of { HEAD ~ this invention } is used in { TAIL ~ the contingency } that the tieback threads in the casing hanger become damaged
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH