Extremely tough and very durable steel bearing with a little boost in performance over ABEC-3 bearings.
Grade 5 chromium steel balls are within 5/1,000,000″ round. These are military level specification, used for precision equipment. R-64 hardness, of the highest grade. 52100 high carbon chromium alloy races go through a vacuum de-gassing process resulting in the purest chromium alloy steel, hardened to R-62. Nylon with graphite retainers are virtually frictionless while providing constant lubrication.