General Tools & Instruments 195-1/2 1/2-Inch Countersink Bit
This high speed countersink has a 5 flute rose pattern for chatter free countersinking on steel, brass, aluminum, plastic, wood, and other materials.  It is made of high-speed steel with five flutes.  82 degree point angle.  It has a 1/4" round shank in size 1/2".