The top ply has a wall formed therein which interlocks with {HEAD ~ the bottom ply wall} to cover and close {TAIL ~ the well} 
to cover
The top ply has a wall formed therein which interlocks with { HEAD ~ the bottom ply wall } to cover and close { TAIL ~ the well }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL