There are numerous archive posts about tuning pin thicknesses and the appropriate drill bit sizes.  Previous posts from Bill Jurgenson seem to suggest a drill size at least 0.1 mm less than the pin thickness.  Of course he also counsels making some trial holes, using an off-cut saved from when the pinblock was cut to size.

I found Bill's advice spot-on for my first building project.  At the time I did not have a good local source for number drill bits (since remedied), so for my 4.5 mm tuning pins I used an 11/64" drill bit (4.37 mm) instead of the #17 that might have also worked (4.39 mm).  The holes were a bit tight at first but loosened slightly over time.  They've remained fine since then.

BM

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