Torque repeatability via torque-limiting ratchets or sleeves
A micrometer reading is not accurate if the thimble is over or under torqued. A useful feature of many micrometers is the inclusion of a torque-limiting device on the thimble—either a spring-loaded ratchet or a friction sleeve. Without this device, workers may overtighten the micrometer on the work, causing the mechanical advantage of the screw to squeeze the material or tighten the screw threads, giving an inaccurate measurement. However, with a thimble that will ratchet or friction slip at a certain torque, the micrometer will not continue to advance once sufficient resistance is encountered. This results in greater accuracy and repeatability of measurements—most especially for low-skilled or semi-skilled workers, who may not have developed the light, consistent touch of a skilled user.