If you’re unsure about the appropriate size for a counterbore hole when using ISO cheese head fasteners, look no further. This brief guide provides you with the precise dimensions you need for your screws and bolts. You can refer to the chart below for easy reference.
A counterbored hole is typically used when you need the top of a screw or bolt to be flush with or slightly below the surface of the material into which it is being inserted. For example, a screw with a counterbored hole sits flush with the surface, whereas a screw with a simple clearance hole protrudes above the surface.
To help you understand the dimensions required for different ISO cheese head fasteners, use the image and the chart provided below. All dimensions are in millimeters.
For instance, if you’re working with an ISO M6 cheese head screw and need a standard fit counterbored hole, you should use a pilot hole with a diameter of 6.6 mm, a counterbore diameter of 11 mm, and a counterbore depth of 4.5 mm.
Counterbore Hole Size Chart for Cheese Head Fasteners (ISO)
| Fastener Size | Pilot Hole Diameter (Close Fit H12) | Pilot Hole Diameter (Normal Fit H13) | Pilot Hole Diameter (Loose Fit H14) | Counterbore Diameter | Counterbore Depth |
| M1.6 | 1.7 mm | 1.8 mm | 2 mm | 3.5 mm | 1.5 mm |
| M2 | 2.2 mm | 2.4 mm | 2.6 mm | 4.4 mm | 1.8 mm |
| M2.5 | 2.7 mm | 2.9 mm | 3.1 mm | 5.5 mm | 2.2 mm |
| M3 | 3.2 mm | 3.4 mm | 3.6 mm | 6.5 mm | 2.4 mm |
| M4 | 4.3 mm | 4.5 mm | 4.8 mm | 8 mm | 3 mm |
| M5 | 5.3 mm | 5.5 mm | 5.8 mm | 10 mm | 3.7 mm |
| M6 | 6.4 mm | 6.6 mm | 7 mm | 11 mm | 4.5 mm |
| M8 | 8.4 mm | 9 mm | 10 mm | 15 mm | 5.6 mm |
| M10 | 10.5 mm | 11 mm | 12 mm | 18 mm | 6.6 mm |