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  • stevecowles

How to use a micrometer

I have wanted to measure the thickness of the disc brake rotors on my bike for a long time to see if they need replacing. The problem is they wear in the centre rather than on the outside so I can’t use my digital callipers.


I’ve solved this by purchasing a generic external micrometer from eBay, surprisingly cheap at just £6.99. It claims to be accurate to 0.01mm, I’m a little sceptical about that but it will certainly be accurate enough for my requirements.

The tool is actually quite nicely made and can be adjusted until it is close using the knurled shaft and there is then a smaller knurled knob to complete the measurement. There is also a lock to prevent it from getting changed accidentally before it is read.

I’ve not used one of these since I was at school and I left in 1979 so time for a refresher. If you zoom in you will see that the measurement shown in this example is 7.75mm and I’ve shown how I got there in stages.


The good news is that I have plenty of wear left in the rotors on my bikes and knowing this has saved me from replacing them and saved me the cost of the micrometer several times over. Nice one.

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