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