The end of the plug adjacent the threaded opening has a hexagonal square or circular exterior for reception of a wrench for connecting {HEAD ~ the plug} to {TAIL ~ the flange opening} 
to
The end of the plug adjacent the threaded opening has a hexagonal square or circular exterior for reception of a wrench for connecting { HEAD ~ the plug } to { TAIL ~ the flange opening }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL