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