Trust SPI's precision blade micrometers for measuring the groove diameter of shafts, keyways, and other hard-to-reach areas. Blade thickness of 0.03 inch, blade length of 1/4 inch. With ratchet stop thimble and nonrotating spindle. Measurement range is from 2 inches to 3 inches with 0.0001 inch graduations and 0.0002 inch accuracy. Micrometer includes calibration standard (for micrometers above the 0 to 1 inch range), short form calibration certificate, and fitted case.