These micrometers come with a calibration certificate traceable to NIST that states they've passed a test for accuracy. All micrometers have a thimble with a constant-force mechanism, so that once the spindle contacts the surface of the measured object, it will stop tightening. This ensures repeatable measurements and prevents over-tightening.

Friction thimbles continue to turn with resistance when the micrometer’s spindle stops tightening.