As described, the testing apparatus rod and {TAIL ~ mandrel} threads into and pulls on the expander member of {HEAD ~ the ribbed plug} 
As described , the testing apparatus rod and { TAIL ~ mandrel } threads into and pulls on the expander member of { HEAD ~ the ribbed plug }
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD