12.5mm ‐ 150mm diameter in 12.5mm increments. Case hardened, stablilized, ground and lapped to +/‐ .0001" or +/‐.0025mm. Micrometer Set Masters are used to calibrate and set micrometers.Micrometer Set Masters are used to calibrate and set micrometers. The master is superior to gage block calibration because they do not require block stackso it is much faster to inspect the linear range of the tool. Micrometer Set Masters indicate the wear on the micrometer anvil because they replicate how the micrometer is used.