Thread Dial Indicator Calculator

This tool can be used to work out whether your thread dial indicator can be used for a particular thread pitch. It automatically generates a table of standard pitches when you click "Calculate" (or change a value and then switch to a different field). You can also input a specific thread pitch that you're interested in and the calculator will tell you whether your thread dial indicator is suitable. If you select your lathe and then select the "Custom" lathe, you can also tweak parameters (e.g. the number of dial indicator gear teeth) to see what dial indicator you'd need to do a non-standard pitch.

I originally decided to work out the maths for thread dial indicators after having some issues with the thread dial indicator on the mini-lathe (mainly that the manual's wrong and you can't use it for 1.25 mm pitch threads). However, it has since been useful for working out whether I could use the indicator on unusual pitches like 4.5 mm. Therefore I thought I'd make it available to others as well.

If your lathe is not included in the list below (or the thread dial indicator diagram looks different to the one on your lathe), you can use the "Custom" setting and tweak to your heart's content. However, an even better option would be to get in touch and let me know the details for your lathe: I can then add it to the list of supported machines.

The details I need are:

  • The manufacturer and model of your lathe.
  • The pitch of the lead-screw (or TPI if it's an imperial machine).
  • The number of teeth on the thread dial indicator gear that engages with the lead-screw (if your lathe has multiple interchangeable gear options, then please let me know all of them).
  • The number of scribed lines on the thread dial indicator face.
  • Whether all of the scribed lines have numbers (if you're not sure what I mean by this, select the Sieg SC2 Metric option below and look at the picture of the indicator: this indicator has 16 lines but the numbers only go up to 8).
  • If at all possible the same information for the version of your lathe that uses the other unit system.

As an example of the last point, I have the metric version of the Harrison M250 but the manual gives enough information that I could work out all the parameters for the imperial version as well. If you can also do this too then it is likely to help others using this site.

Lead Screw
Pitch (mm)
Thread Dial Indicator Gear Teeth:
Lines on Thread Dial Indicator:
Line Marking:
Use this if you want to use a pitch that isn't in the table below:
Pitch (mm)
Used Gear:
Valid Lines:

This website is free, but costs me money to run. If you'd like to support this site, please consider making a small donation or sending me a message to let me know what you liked or found useful.