true that the grades designate "sphereicity" if that's the word, i.e. how close the tolerance from perfectly spherical, and the level of surface polish, but the ones I buy that are called "Grade 25" also specify their material and hardening treatment ("hardened chromium-steel alloy" noting they don't say "case-hardened" nor if there's nickel in that alloy)
ll of which could be BS but I get them cheap enough in quantity I willingly takes my chances.
YMMV