Pick a handful of replacement stud ("main/top") gears for an imperial quick-change lathe that, combined with the existing TPI dial, most nearly approximate standard metric thread pitches.
On a quick-change gearbox lathe, the dial's TPI reading is only exact for the factory stud gear. Swap the stud gear for one with R teeth (factory has F teeth) and the whole gear train scales by R/F, so the pitch actually cut at dial setting T is:
pitch (mm) = 25.4 × (R / F) / T
This tool scans every candidate replacement gear against every TPI setting your gearbox offers, and picks a small set of gears that together get closest to the standard metric pitches — biased toward fewer teeth to cut, and treating your factory gear as free (no cutting required).