I was scrounging through one of my many machinist chests yesterday looking for some small drill bits I'd seen awhile ago (still haven't found them) and ran across a metal tin full of miniature reamers and cutting tools with tapered shanks. In 50 years of machining/tool making I've never seen anything that would accept these bits. Measuring the diameters it occurred to me that they might fit a tool for clock repair. The reamers are around the sizes of pivot holes and the ball nosed cutter looks like it'd make oil wells. Maybe these fit a watchmakers lathe?