For drilling, enlarging and de-burring holes in thin sheet metal up to a thickness of 2mm. High quality M2 grade High Speed Steel (HSS) 3 flat shank to prevent slipping in the chuck" Diameter mm: 16.0: 31.0 Shank Dia. mm: 9.5 Shank Type: Three Flat Material: M2 Grade HSS Steel To Fit Screw Dia. mm: N/A Timco Cone Cutter (Size 16-31mm - 1 Each) in Silver