These engineering quality countersinks drill a precise recess to allow a fastener head to sit flush in alloy and non-alloy metals, timber and man-made boards. 90 head angle High quality M2 grade High Speed Steel (HSS) 3 flat shank to prevent slipping in the chuck" Diameter mm: 16.5 Shank Dia. mm: 9.5 Shank Type: Three Flat Material: M2 Grade HSS Steel To Fit Screw Dia. mm: 8.0 Timco 3 Flute Countersink (Size 16.5mm - 1 Each) in Silver