Cutting ToolsConsumable
Countersink
A conical cutter that opens the top of a drilled hole to match a countersunk head, so the fastener finishes flush with the surface.
What it does
- Cutting a seat for a countersunk head screw
- Deburring a drilled hole
- Opening a hole to take a flat or oval head
Materialswhat it is used on
All materialsWhat to look forthe judgement calls, before the spec sheet
- The included angle has to match the head. Metric countersunk heads are 90°; some inch series use 82°, and the two do not seat on each other — a mismatched pair leaves the head standing proud on a ring of contact.
- Diameter should clear the head, not merely meet it. A countersink the same size as the head gives line contact and crushes the surface.
- For repeat work, a piloted or micro-stop countersink controls depth instead of relying on feel.
Misuse and safetythe ways this tool causes rework
- Countersinking cuts a very thin section, so it chatters easily. Slow speed and steady pressure is the whole technique.
- On a thin sheet a countersink removes most of the material and the head pulls through. Use a dimple or a rivet nut instead of cutting the sheet away.
Projects that call for itand what it is doing on each one
All projectsFrequently asked questions
What angle countersink do I need?
90° for ISO metric countersunk head screws. Check the standard page for the head geometry before cutting — a mismatched angle shows as a head that will not sit flush however hard you tighten it.
Can I countersink with a drill bit?
A large bit can approximate it in soft material, but the angle is set by the point geometry and is rarely the 90° the head wants. For a head that has to finish flush, use the cutter made for it.