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ABEC-3 tolerances and noise tested - Grade 10 Chromium Steel Balls - High precision balls are within 10/1,000,000 round, twice as round as the industry standard, at its highest level. 52100 High Carbon Chromium Alloy Races - Vacuum de-gassed process for the purest chromium alloy steel, hardened to R-62, extremely tough and very durable. Polished to a mirror finish for ABEC-3 precision and noiseless movement. Riveted Steel Retainer for toughness