How to Use and Read an Outside Micrometer

Reviewed by Anne Schmidt

Last Updated: December 17, 2024 Fact Checked

If you are a machinist, manufacturing, or engine professional, exact measurements are an everyday must. When it comes to measuring cylindrical or spherical objects, an outside micrometer would be the best tool to use. A well calibrated micrometer can be difficult to use, but with patience and practice, this tool can be a part of your skill set.

Method 1

Method 1 of 3:

Measuring with the Micrometer

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1
Familiarize yourself with the anatomy of a micrometer. Some parts are stationary while others are movable. ^{[1]
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- Ratchet stop
- Thimble
- Frame
- Thimble lock
- Spindle
- Anvil
- Sleeve
2
Clean the anvil and spindle before beginning. Use either a clean sheet of paper or soft cloth, and hold it between the anvil and the spindle. Gently twist and close on the sheet or cloth. Slowly, pull out the sheet or the cloth.
- This practice isn't a necessary step for measuring, but keeping the surfaces of the anvil and spindle clean ensures precise measurements.
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The anvil is stationary and can withstand more pressure than the spindle. Make sure the object doesn't move or scratch the surface of the anvil.
4
Hold the micrometer with your right hand. The frame will rest gently on your palm.
- You can also fasten the frame on a stationary vise; this helps free up both hands for the measuring process.
Be sure the 0 on the thimble is lined up with the scale on the sleeve.
Apply enough force. The thimble often clicks. Three clicks is a good stopping point.
Even though it is on lock, the spindle can still be moved. ^{[2]
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Be sure to avoid scratching either surfaces of the anvil or spindle; the slightest scratch can ruin the micrometers measuring accuracy.
If the spindle loosens, be sure to remeasure.

Method 2

Method 2 of 3:

Reading an Inch Micrometer

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1
Learn the different number scales on the thimbles.
- On the sleeve is a scale that measures by the one-hundred thousands or 1/10 of an inch; in decimal form it would be .100.
- In between those whole numbers are three lines that represent twenty-five thousandths of an inch; in decimal form, it would look like .025.
- The thimble has evenly spaced lines that represent one-thousandth of an inch; in decimal form it would be .001.
- Above the whole number scale on the sleeve are lines that measure to ten-thousandths of an inch; in decimal form it looks like .0001.
The last visible number will read as the thousandths. For example, if the last number you can see on the sleeve is 5, then it would read 500 thousandths, or .00005.
Look at the individual markings exposed next to the 100 thousandths and multiply each marking by .25.. In this case 1 x .025 would be .025.
If it's closest to 1, then it would be .001.
In this case it would be .500 + .025 + .001 = .526.
Read that line that lines closest with the sleeve. If, for example, it lines with 1, then the measurement will will read .5261

Method 3

Method 3 of 3:

Reading a Metric Micrometer

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1
Learn the different number scales on the thimbles.
- The line on the sleeve usually has top line showing millimeters, and below that line the marks represent half millimeters.
- The marks on the thimble usually go to 50, and each line represents a hundredth of a millimeter or .01 mm.
- The horizontal lines above the scale on the sleeve will measure to the thousandth of a millimeter, or .001 mm.
If the last line you saw were a 5, then you would have 5 mm thus far. ^{[3]
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3
Incorporate all the half millimeters in your measurement. If you have one mark that would be .5 mm.
- Don't count a mark that is barely showing; the reading on the thimble might be getting close to 50.
If the line on the thimble reads 33, then you'd have .33 mm.
In this example, add 5 + .5 + .33. The measurement is 5.83 mm. ^{[4]
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6
Add the thousandths. If the thousandths read a 6, then at .006 to the measurement. In this example, it would be 5.836
- The main time you should incorporate the thousandths measurement is if the object has less tolerance for the pressure applied by the micrometer.

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Question

How do you measure a bearing's half-thickness?

Community Answer

Use a ball bearing on the inside then subtract the ball bearing diameter from the overall dimension of the ball bearing and the plain bearing shell.

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What are micrometers used for in mechanics?

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The most common use I can think of would be measuring piston diameter and inside of cylinder bore to check wear. There are probably many other uses, thickness of shims, wear of transmission parts, thickness of break rotors, etc.

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How do I clean an inside micrometer?

Gerald Phillip Harvey

Community Answer

A piece of paper or a soft cloth close the spindle, gently pulling the paper or cloth out.

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Tips

Remember also that an outside micrometer, when used correctly, is much more accurate than calipers.

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Practice -- you will develop a "touch" or "feel" for it.

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Measure the desired object multiple times as a check on your work.

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Warnings

It is assumed when a micrometer is used, that an accurate and precise measurement is desired. Ensure your micrometer is properly calibrated. They do lose accuracy with use, and must be adjusted every 36 months according to NIST. Check more often when frequently used.

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Things You'll Need

Micrometer
Micrometer tools:
- Standard – The standard is an item of precisely calibrated length and flatness which is used to verify the accuracy of the micrometer or to reset it if it is found to be inaccurate. Standards are typically a round or rectangular piece of steel. They are employed just prior to using a micrometer or may be used on a set schedule as part of a calibration program.
- Wrench – insert in hole on back of the stock to adjust the micrometer if needed.

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How to Use and Read an Outside Micrometer

Steps

Measuring with the Micrometer

Reading an Inch Micrometer

Reading a Metric Micrometer

Community Q&A

Video

Tips

Warnings

Things You'll Need

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