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