For this purpose, a nitride layer having {HEAD ~ a hardness} of {TAIL ~ Hv} 650 or more at a thickness of 3 mum or more and 15 mum or less is formed on the surface of a cage 
of
For this purpose , a nitride layer having { HEAD ~ a hardness } of { TAIL ~ Hv } 650 or more at a thickness of 3 mum or more and 15 mum or less is formed on the surface of a cage
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH