Does anyone know what the threading on a typical modern-ish stem binder bolt is? I just measured a Nitto Technomic and the unthreaded portion of the bolt seems to be about 7mm, while the major diameter of the threaded portion is about 8mm. Presumably the bolt has rolled threads, since their diameter is greater than that of the shank. Not clear to me whether the threading itself is a standard M8 threading, since I don't have a bolt of that size on hand, or a thread gauge.

I have a reason for wanting to know this but will not bother to explain, partly to save time and partly so no one will try to talk me out of the project I'm contemplating.

Yes you are describing a rolled thread , spokes are rolled threads..

thread rollers press down, making the groove valleys,
and displacing metal up , in pushing metal up, forming the peaks.

in the case of the stem quill bolt,
The steel was probably next, heat treated, then chrome plated..

Probably M8..

...

My Technomic's bolt is M8 x 1.25, verified with thread die and thread pitch gauge.

Thanks!