Flat Head Screw Reference

Why Flat Head Screw Data Matters

Flat head screws sit flush with the surface, but only if the countersink matches the head angle and diameter. The two common standards — 82-degree (ANSI) and 90-degree (metric/aerospace) — have different head dimensions that directly drive your countersink depth.

• Head diameter determines the countersink diameter — always check the max head size for your screw
• 82-degree flat heads (ASME B18.6.3) are standard for inch fasteners; 90-degree is used in metric and aerospace
• Under-sized countersinks prevent the screw from seating flush; over-sized ones leave a gap around the head

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