Lost nut from victrola speed indicator

[johnwilla]

I took my 4-spring orthophonic motor out of the credenza today, and in the course of that I removed the nut holding the speed pointer on to its shaft. Of course, I cannot now find the little nut--it doesn't seem to be a standard size that, e.g., knurled nuts for clock hands will match. Anybody suggest a replacement source? Or give me a size for this little nut?
Thanks in advance for your thoughts--