0.00 micron surface smoothness Use to calibrate inside micrometers at either the high or low end of the range Also ideal for dial bore gages, vernier/dial/electronic calipers, and other gages Actual size is engraved on each setting ring SPI 10-719-3 Setting Ring: 1/2" Inside Diameter x 1-1/2" Outside Diameter x 0.393" Thick, Accurate to 0.0001", 10.00micro m Surface Smoothness. Use to calibrate inside micrometers at either the high or low end of the range. Also ideal for dial bore gages, vernier/dial/electronic calipers, and other gages. Actual size is engraved on each setting ring.