Depth micrometers (mic) often times have the ability to measure between 0″ – 6″ as seen in this photo above I am measuring a die with the aide of a 123 Block. The mic in this case is showing a measurement of .163 which means the die itself is 1.000 – .163 = .837. The math is simple. The question becomes how does one measure depths greater than 1.000 at this point. That is easy. I will walk you through changing the rods in a depth mic.
In order to do this you will need the small spanner wrench that came with your depth mic.
You will see a small hole in the top of your depth mic. This is where you will put the tip of the spanner wrench.
Turning the top counter clockwise you will find that it comes right off. It is important to note that you do this in a clean environment in order to prevent debris from getting into the fine threads.
The rod assembly will pull out with no issues at this point.
Now place the new rod back into the depth mic.
Now place the head of the depth mic back on and tighten it with the spanner wrench. It is important to note that you don’t over tighten the head. I am able to tighten it using one finger as shown in the photo.
At this point I am ready to measure the die again.
You can see that I am using the 2.000 side of the 123 Block now as the measuring base where as before I was using the 1.000 side. I now obtain a measurement of 1.161. I know this because I inserted the 2.000 rod into my depth mic which gives me the 1.000 portion. Followed by the measurement of .161 from the mic itself. This gives me 1.000 + .161 = 1.161, which in return means the die is .839 tall on this side. This was found by taking 2.000 – 1.161 = .839. As you can see changing rods doesn’t affect the accuracy of a depth mic.