SPI Vernier Micrometer Head Use for improving accuracy in machines, gaging, test equipment, electronics, optical instruments and machine instruments. Features include... 0-.5" Measuring Range 0.001" Graduations + 0.0002" Accuracy 0.51" Thimble Diameter 0.20" Spindle Diameter 2.64" Overall Length With Spindle Lock Flat Spindle Face Certificate of Calibration