Tripod mounting threads
There are two standard tripod screw threads:
a 1/4-20 UNC and 3/8-16 UNC (20 means 20 threads per inch, 16 - 16 threads per inch)
You can find more about these threads here (ISO standards):
Both threads are also the same pitch as the old UK "Whitworth" thread form, 20 TPI for 1/4 inch and 16 TPI for 3/8 inch.
If your engineer friend has a stock of old Whitworth taps and dies he should be able to use those.
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