The vast majority of countersinks are designed for working on steel and have three or more flutes. For softer materials like wood, plastics and yellow metals, a single flute design is preferable because it can't develop a resonance - the cause of chatter and triangular countersunk holes.
Made in Japan from high speed steel, this single flute countersink produces beautifully smooth, concentric conical countersunk holes.
Satisfyingly over specified for woodworking, if it does end up being inadvertently used on unhardened steel it is unlikely to sustain damage. It also performs superbly on brass, bronze, aluminium and plastics.