The groove includes a central concave portion and {TAIL ~ two support surfaces} extending downwardly from {HEAD ~ respective sides} of the concave portion 
The groove includes a central concave portion and { TAIL ~ two support surfaces } extending downwardly from { HEAD ~ respective sides } of the concave portion
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH