powdercoat can be very thin (so yes, less than 1mm), but i would not want to have any p/c on any surface where bolts will be, or where the face will be meeting another important piece via bolt. it just seems like a spot where something could go wrong. at my old moped shop, we would get frames powdercoated all the time, and we found that a lot of "contact" spots, when coated, would create mating issues. of course, these little two-strokes vibrated like crazy so that was a HUGE part of the problem.