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