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