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