Countersunk (flat head) screw

ISO 10642 (hex), DIN 965 (Phillips), DIN 963 (slotted)

Sizes

M2-M20

Drive & head

Internal hex, Torx, Phillips or slotted

Materials

Alloy steel, A2/A4 stainless

Strength / grades

10.9, 12.9 steel; A2-70 stainless

Hole and pilot guidance

Metric countersinks are 90 degrees; the recess diameter must match the head so it lands flush.

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Flush machine covers and brackets

Head sinks level with the surface so nothing snags

US 82-degree and metric 90-degree countersinks do not seat properly in each other.
Over-tightening a countersunk screw can crack brittle plastic or thin castings.
You cannot countersink into sheet that is thinner than the head depth.