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