Countersink fit chart.

A countersink is a cone cut to the screw head's angle, ending in a straight through-hole. What decides whether it works is the material left under the cone — the land.

Land = sheet thickness − cone depth. With at least 0.010″ of land the head seats flush and square. With less, the bottom of the cone becomes a razor ring that burrs, deforms under the screw and never seats. If the cone is deeper than the sheet, it cuts out the far face and the head pulls through.

On the chart every horizontal line is a countersink at its cone depth, and every vertical line is a gauge we stock in the grade you chart. Where they cross, the dot says whether that screw seats at that gauge. The green region is safe; the amber band is the knife edge; above the top line the cone breaks through.

Minimum sheet = cone depth + 0.010″. The last column is the thinnest gauge we stock, in any grade that offers countersinking, that meets it.

Not offered: MIC-6 cast plate, AR500, Spring steel 1075 / 1095. Full countersink dimensions are in the countersink size chart; for any angle and diameter, use the countersink calculator.