The Ultimate Guide to Micrometers

Micrometers, often called “mics”, are likely to be the most utilized precision measuring instrument in any machine shop. As they typically measure in .0001” increments (or .01mm for metric models), micrometers provide extremely accurate measurements and machinists often prefer them to other devices such as calipers.  

• ANVIL: Together with the spindle, the anvil is the part that will be in constantly in contact with the part and therefore the most likely to chip. For this reason, good models usually feature a carbide-tipped anvil that will allow for longer tool life.
• FRAME: Frames come in a number of different sizes and shapes. Some shapes are designed for specific uses. The hub micrometer in the image below, for example, is designed to get into really small areas. When choosing a micrometer, always consider the type of part you are going to measure.
• LOCK NUT: A spindle lock is handy to keep track of a measurement and also to lock the spindle for small lot gaging. Some micrometers have a lock nut (as shown), whilst others may have a locking lever. We recommend choosing the lever type as it seems to require less attention over the years and it’s easier to operate
• SLEEVE SCALES: While all micrometers feature the main index scale on the sleeve, which measures in increments of .025”, the most accurate models also have a Vernier scale for more accurate measurements. Vernier scales measure in .0001”.
• RATCHET SPEEDER: Many mics have a sort of slipping clutch mechanism that prevents over-tightening and aids the user to apply a constant measuring force to the spindle, helping to ensure reliable measurements. It’s not a life-changing feature, but it’s something to consider, especially important in production situations, with different operators, but one QC spec.