Sub-zero treatment (Cryogenic hardened) Use Ring Gauge as master gauge for "0" adjustment of measuring tools such as bore gauge, inside micrometer, dial caliper, etc. Actual Size 0-30mm, Tolerance +/-1.0um Actual Size 30-50mm, Tolerance +/-1.5um Actual Size 50-100mm, Tolerance +/-2.0um Actual Size 100-200mm, Tolerance +/-5.0um Hardness HV 653-772