For a flush fit every time, these gauges ensure your fastener and countersink mate perfectly for a secure hold. These gauges are often used to verify the top diameter and angle of holes in precision assemblies. They’re preferred over chamfer gauges, which also measure diameter but don’t check countersink angle. When the conical probe touches the hole’s angled walls, the diameter will display on the dial.

To verify the countersink angle, feel how snug the probe fits into the hole. You’ll also know the angle is incorrect when the reading for the top diameter is a different value than expected. Choose a gauge with an angle that matches that of your hole.