Originally Posted by HillRider

You are agonizing over minutia and there are no "bike specific" bearing balls.

AISI 420 is a hardenable stainless steel tool steel and is unnecessary for bicycle bearings. 316 is a high Ni/ high Cr stainless that cannot be heat treated and is used only where corrosion resistance trumps all other considerations. There is no need for it for bicycle bearings.

Most good quality bearing balls for standard service are AISI 52100 grade Cr steel and that is more than adequate for bike use. Grade 25 refers to roundness and is, again, a more than adequate quality. For that matter Grade 100 or even 200 balls (not as round) would be adequate.