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