A screw head shaped as an inverted cone with a flat top, designed to finish flush with or below the surface in a countersunk hole. Inch flat heads use an 82 degree included angle and metric ones 90 degrees, and mixing them leaves the head bearing on a thin ring at the top or bottom of the seat. Flat heads center themselves in the countersink, which helps alignment but can fight a mating hole that is slightly out of position.
These are metric flat heads, so the countersink needs to be ninety degrees, not the eighty-two you've got in the drill.
Also heard as
- FHCS
- countersunk screw
- flat head socket cap screw
Related terms
SHCS
Socket head cap screw: a round-headed, high-strength screw driven with a hex key into a tapped hole.
Phillips
A cross-shaped recess drive with tapered walls, the default drive on sheet metal, wood and small machine screws.
Torx
A six-lobed star drive that transmits more torque with less cam-out than cross or hex recesses.