A threaded mandrel goes through {HEAD ~ the hole} in the top of the cup shaped member and engages the expander member of {TAIL ~ the rib plug} 
A threaded mandrel goes through { HEAD ~ the hole } in the top of the cup shaped member and engages the expander member of { TAIL ~ the rib plug }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL