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