Industry Standard Grade 100 420 Stainless Ball Bearings: High Quality Graded 420 Stainless Steel Ball bearings made from
420 Stainless Steel with a hardness of 52 -55 HRC Rockwell Scale, the hardness is all the way through the ball.
These are the same stainless 420 steel balls used to manufacture bearing assemblies and have a high duty and life cycle.