I've been building a cheap Chinese Uke kit. The holes for the tuning machines were ugly, and the provided bushings were little more than flat plastic washers. This bushing fits all the way into the drilled holes and helps center the machines. ID is 6mm and OD is 7.2mm depending in your printer. I always use a bit of horizontal expansion when I print stuff that needs a tolerance.
white, but hey, its your bushing.