A countersink cuts the cone that lets a flat-head screw finish flush with the surface. The whole job is decided by one number: the included angle, which has to match the fastener, not the drawing’s idea of a chamfer.
Pick the angle first
82° — the standard for inch flat-head machine screws and wood screws in the US.
90° — the metric equivalent, and the usual choice for deburring and for chamfering a hole before tapping.
60° — center-drilling work, lathe centers, and lead chamfers where a shallower cone would leave too wide a mouth.
One flute or three
The single-flute countersink has one cutting edge through a cross hole. It has nowhere for a chip to stack up and it does not chatter the way a multi-flute tool does on a thin sheet or an interrupted entry, which is why it is the deburring tool of choice. The three-flute version cuts more evenly and leaves a better finish on a seat that has to bear a fastener head squarely, and it holds the angle better over a production run.
What is in this range
Included angles: 60°, 82° and 90°
Flutes: 1 and 3
Material: high-speed steel
Finishes: bright (uncoated), TiN-V, TiCN-PG and TiAlN-HC
