DF-1680T 8.0mm HSCO Titanium Spot Weld Drill Bit for High Strength Steels -This is the most popular spot weld drill bit. 8.0mm or 5/16th is the most common size of spot welds that need to be removed. The Titanium coating on this bit will help prevent the bit from dulling due to overheating. The twist is the same size as the shank which is also 8.0mm and has a flat spot on it to be tightened into the DF-15 Series Spot Weld Drills. These drill bits a specifically designed for the abuse of spot weld drilling. Flat ground for strength, centering nib to prevent walking. German made spot weld bits are available in 3 sizes, 6.5, 8.0 and 10.0 mm. These Cobalt high-speed steel mix bits are 45mm long and work with all brands of spot-weld drills. Titanium (gold color) is a heat resistant coating that extends drill life by about 50%.