Clamp-On Countersink: Two Blocks Screwed Round Any Drill, Twin Cutters Countersink the Hole as It Is Bored (Brackin, 1903)

George W. Brackin of Philadelphia received US 727,580, dated 12 May 1903, for a countersink that clamps onto a drill or auger bit. Two blocks are screwed together across the bit at any point along it. A twin cutter is screwed into an inclined seat in each block, its point reaching into the bit's flutes. As the bit bores, the cutters arrive and cut the cone for the screw head without taking the bit out. A slotted stop sets how deep it goes, so it gauges the hole too. We make three for 4, 5 and 6 mm drills. The patent gives no sizes; every size here is ours.