Which hardware besides the regulator, and what year? There are probably a couple different sizes used in each assembly; and I'd bet they changed at least once between 1964-1/2 and 1973!
IIRC - StDr is right, which is why I packaged ALL of my door hardware together when I stripped it down...........now if I could just find the damned zip-loc!
I believe they're 3/8" and 1/2" bolts.................
Without being too general, pretty much all my '68's door bolts for the wind wings, adjuster bolts, and such were 5/16-18. But since you didn't specify what kind of car, my Mazda pickup has lots of 6mm bolts holding the exits together.