Features. This Cobalt high speed steel mix bit is 45 mm. long and works with all brands of spot weld drills. This German made bit may be used with off brand spot weld drills. The twist is smaller than the shank which is 8.0 mm. and has a flat spot on it to be tightened into our DF-15 series Spot Weld Drills. Specfically designed for the abuse of spot weld drilling. Flat ground for strength, centering nib to prevent walking