These micrometers come with interchangeable anvils of varying lengths, giving them a wide measuring range. All have a ratchet 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. When the spindle stops tightening, the thimble will continue turning with a clicking sound. A speeder knob reduces the time it takes to open and close the micrometer.