Zaph, 36mm Forstner Bit...

[critofur]

36mm Carbide Forsner bit

Not cheap, but, if I was going to make more than a few pairs of speakers with the ND20 tweeter I guess I'd get one? (if the fit would be snug but not too tight to fit)

 

[Zaph]

Congrats, that's the first 36mm I'm seen. That should be perfect. But, I'd have to be mounting about 100 of these to make that bit worthwhile. (Anyone building a line array with these tweeters, take note) But for the average guy, a cheaper 1-7/16 is better. I've got a 1-3/8" that works but is a little sanding intensive.

 

[Cataclysm]

If you knew someone with a lathe, it's literally a 2 minute job to just turn the major diameter of an oversized, imperial forstner bit down to spec. A viable, cheaper, and faster route of going.

Heck, depending on the type of forstner you have, you can run a file along it while it rotates at a low speed in your drill press; effectively turning it down to whatever diameter you desire. Just clean up the teeth and chip removers with some small needle files when you're done!

 

[critofur]

Cheaper [but still carbide tip] 36mm Forstner bit

File huh? Diamond file?

Found a much cheaper source, I THINK this is a 36mm bit - I'm not certain if the 36mm is the width of the hole, but I think so?:

Southeast Tool SEHB5736RH - Hinge Drill Bit, 36mm Dia., 10mm Shank

Price seems good, anyway.