Thread size of clock knob nut

[Fred]

I verified that two of my clocks have a 1-72 thread. A M1.6 screw slips inside the nut. A .35mm pitch works out to 72.6 TPI so that might work.
Maybe some clocks are metric

Thanks for your input ws23rt. 1-72 is spot on.  

I am glad this got worked out Fred. I learned a few things about measuring these small threads doing this. Kind of like sudoku puzzles. The answer by exclusion confirms the test.
Hope you don't break many taps

 I'll let you know.  I have broken off a few in the past and they were larger so this will be a bit of a test. Hopefully I've learned from my mistakes.