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Counterboring Guidelines
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Counterboring creates a flat-bottom recess around a hole so a screw head can sit below or flush with the surface of the part. This is most commonly used for standard socket head cap screws (SHCS) and other machine screws where the head needs clearance from a mating part, moving assembly, or finished outside surface.
Unlike countersinking, counterboring keeps a cylindrical wall and flat shoulder for the screw head instead of a tapered seat. Use it when your hardware has a cylindrical head or when you need a predictable head pocket depth.
Counterbore Sizes
You can order a counterbore of any depth when the body diameter and pilot diameter match one of the sizes below. Upload a STEP file with the counterbores drawn directly in your model.
The sizes below are the supported counterbore dimensions for common socket head cap screws. Counterbores must be modeled directly in your STEP file; they cannot be added from the hole operations selector.
Inch
| For screw size | Body dia. | Pilot dia. |
|---|---|---|
| #4 | 0.206" | 0.128" |
| #6 | 0.244" | 0.154" |
| #8 | 0.288" | 0.180" |
| #10 | 0.330" | 0.206" |
| 1/4" | 0.398" | 0.266" |
| 5/16" | 0.491" | 0.328" |
Metric
| For screw size | Body dia. | Pilot dia. |
|---|---|---|
| M3 | 6.0 mm | 3.5 mm |
| M4 | 7.5 mm | 4.5 mm |
| M5 | 9.0 mm | 5.5 mm |
| M6 | 10.5 mm | 6.5 mm |
| M8 | 13.5 mm | 8.5 mm |
Depth Tolerance
All counterbores are cut to a depth tolerance of +.015" / -.000".
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