Drill bits may be coated to assist in cutting lubricity and/or add abrasion resistance for longer tool life. Shank types include straight, tapered, reduced, hex, square, and threaded. GOST 26474 - ...

But when a drill bit breaks off flush in a hole, there aren’t a lot of options, especially for a small bit. If the stars align, though, you may follow this video guide to dissolve the drill bit ...