The Ultimate Guide to Micrometers

January 10, 2019 10:00 am

 

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.

 

Anatomy

 

Image credit: megadepot.com

 

As you can see in the image above, a traditional micrometer is generally composed of several different parts. Here are some important things to consider when choosing a micrometer:

 

  • 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.

 

Digital vs analog

Newer models, the digital micrometers, have a digital display that makes it easier for you to read measurements. In terms of digital vs. an analog micrometer, there is not much difference in accuracy. Digital mics, however, offer two significant advantages: resolution and quick scale conversion.

The displays on most digital electronic micrometers, in fact, resolve to 0.00005″ and can be quickly converted from imperial to metric and vice-versa.

Since there’s not much difference between the two models, we usually recommend going with the most convenient option, which is generally the analog one.

If you are considering buying a digital mic, this is our recommendation.

 

Types of micrometers 

 

As already mentioned about, mics come in different sizes and shapes according to their intended use. Here are the three main types of micrometers that you will encounter when working in a machine shop:

 

 

Outside micrometer

Brown & Sharpe 599-1-31-9 Chrome Framed Outside Micrometer

The most widely used type if micrometer. It’s used to measure the distance between two external points of either round materials if you are working on a lathe, or square materials if you are working on a milling machine.

 

 

Inside micrometer

Mitutoyo 139-006 Tubular Vernier Inside Micrometer

Designed to take inside measurements, such as the ID of bushings or bearings. The most common models of inside mics look like outside mics without a frame and anvil, but other types, more similar to calipers, are also available.  Unlike outside mics, the read on the sleeve increases as the sleeve expands.

 

 

Depth micrometers

Starrett 449 Vernier Depth Gauges, Micrometer Type

Depth micrometers allow for precise measurement of depth for features like holes, slots, recesses of keyways. The tool has a hardened ground and a lapped base attached to the micrometer head. Like inside mics, the measurement increases as the rod extends into the hole.

 

 

What type of micrometer should you buy?

 

If you are just approaching the trade and thinking about where you should start investing to build your personal toolbox, we definitely recommend starting with the best 0-1’outside mic you can afford, as it’s most likely the tool that you are going to use most. Later on, you might fill in with additional micrometers, like a 0-6” set, but you’ll likely use them less often so we recommend investing more in the first one and settle on cheaper models for the add-ons.

As already mentioned above, mics vary depending on the intended use so the best advice we can give is to identify the type mic that you will be using most (outside, inside or depth) and invest in that.

 

Best models

 

OUTSIDE MICS

Brown & Sharpe 599-1-50 Classicmaster Micrometer

Our favorite model.

  • Carbide anvil
  • .0001” accuracy
  • Locking Lever
  • Friction thimble

 

ORDER NOW

 

 

Mitutoyo 101-117 Outside Micrometer

  • Carbide anvil
  • .0001” accuracy
  • Locking Lever
  • Friction thimble
ORDER NOW

 

 

 

Starrett T444.1XRL-1 Outside Micrometer

A great quality mic, only third in our list due to the lock nut type.

  • Carbide anvil
  • .0001” accuracy
  • Lock Nut
  • Friction thimble
ORDER NOW

 

 

 

INSIDE MICS

Mitutoyo 139-201

Tubular inside mic. It comes with interchangeable rods that allow you to measure ID up to 12”.

ORDER NOW

 

 

 

 

 

Fowler 52-275-005 Xtra-Range Inside Micrometer

More similar to a caliper, the frame is specially designed to enable the micrometer to provide extremely accurate small internal measurements.

ORDER NOW

 

 

 

 

 

 

DEPTH MICS

Starrett 440, 445 Vernier Depth Gauges

Depending on the model, you can measure up to 12” in depth. It comes with a ring-type knurled lock nut, ratchet, and speeder for stability and to apply uniform pressure and make quick adjustments for precise measurements.

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Mitutoyo 129-127 Depth Micrometer

Includes interchangeable 0.157″ diameter measuring rods that can be adjusted in 1″ increments for flexibility up to 4”.

ORDER NOW

 

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7 Comments

  • LocoMarty

    In my years of experience, since 1977, carbide face mics are more prone to being chipped. And in a lifetime of use, non carbide faced mics are not likely to be worn out, if used correctly.

  • Tim

    I have used Starrett, Brown and Sharpe, Mitutoyo, and off brand Polish mikes throughout my machine shop career. You may not like the lock on the Starrett’s, but the feel of them is second to none. Browne and Sharpe have to smooth of a feel, and Mitytoyo are, in my opinion, a step below the Starrett. Surprisingly, the first set I owned, the off brand Polish, were very nice, but you can no longer find these as easily as you could in 1985.

  • juanchus

    very usefull artlce, tanks for this type or information. I espect to go more deep knowlege in it`s issue , see you latter

  • Bob

    I feel that you missed some , such as thread mics and tube wall thickness mics, which would be of interest to those who haven’t met them in their field.

  • Very informative article. May include some detail on use of micrometer (least count, error) and how to read.

    Regards

  • Mike

    Nice job on the micrometer article.
    Now I’d like to see an article on micrometer calibration done by the user. Thank you

  • Murph

    Not a big fan of Carbide anvil mics and still prefer my old hand me down Starrett 0-1 from my uncle Pete from the 50s. They just have a feel like nothing you can buy today.

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