A micrometer is one of the instruments used to measure objects of various small sizes. In this post, we will review the anatomy of a micrometer and how to read them. We will be using a Mitutoyo micrometer as an example.
The frame is typically U-shaped. There are frames that come with a digital read out. It also used to mount the micrometer. Heat can affect the micrometer reading so the frame should be made of a material that can absorb that heat such as plastic.
The anvil is the component that does not move therefore the object that needs to measured will be held there.
The spindle also holds the object that needs to be measured but it moves by rotating the thimble. The spindle should be placed firmly against the object. Internally, the spindle is threaded and connects to a screw.
This clamp is used during measurement reading and locks the object being measured in place for accurate reading. The lock position is towards the spindle.
You can see the primary scale on the sleeve and the thimble rotates around it. The index line is also located on the sleeve for measurement readings.
The thimble is also moveable rotating around the sleeve as mentioned previously. The secondary scale is on the thimble for higher resolution measurement. The surface is knurled for proper gripping while rotating.
At the end of the micrometer is a ratchet stop, this will help with proper reading as well. It ensures that the object is held with the correct pressure – you will hear a clicking sound when turning it to confirm the appropriate pressure.
How to Read A Micrometer
For accurate readings, the micrometer measures best when mounted to avoid any unnecessary heat while being handled. Typically, the frame is used to mount a micrometer.
If you do need to hold by hand, it is recommended to measure with the hand position shown below. Using the micrometer in the field can come in handy.
Tip: When holding by hand use the palm of your hand and a finger to anchor the frame.
The primary scale is located on the sleeve. This scale contains the 1mm increment and half mm increment reading. The second scale is located on the thimble and has 50 marks.
When you are measuring your object only count the exposed marks up to the edge of the thimble.
Thus far in the image we have 7mm.
To measure into the hundredth mm increments, use the index line to meet the mark on the Second Scale on the thimble.
From the example in the image the measurement on the thimble is 0.14mm.
For the total reading simply add the measurement from the primary scale and the measurement from the secondary scale.
7mm + 0.14mm = 7.14 mm
Therefore, the measurement in the image is 7.14 mm.
Tip: If the half mm increment is showing on the primary scale, add 0.5mm to the total reading.
There are a variety of micrometers in the market from simple ones like the Mitutoyo on above to ones with a digital readout and many sizes both in inch and metric. Be sure to check out MISUMI’s line of Mitutoyo measuring instruments from micrometers to surface roughness testers online.