The manufacturing method 1, wherein the sandblasting is performed up to {HEAD ~ a distance} that is smaller than {TAIL ~ a depth} of the groove 
is smaller than
The manufacturing method 1 , wherein the sandblasting is performed up to { HEAD ~ a distance } that is smaller than { TAIL ~ a depth } of the groove
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH