Yep, had a screw go loose on my early 60's snare at a gig, and didn't realize it until I got home.... yuk!

now it seems like this screw (the one at the bottom holding the strainer taut) is not standard or metric threading? Does anybody know about this in detail, OR have tips on where to source replacements? Really trying to keep this all-original and not cave in to the new, and very practical-looking replacement part.