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.

Ratchet-stop thimbles have a speeder knob to reduce the time it takes to open and close the micrometer. When the spindle stops tightening, the thimble stops turning, but the speeder knob will continue turning with a clicking sound.