Scenario table
| # | Units | Bolt size | Fit | Plating (µm) | Extra allowance | Hole Ø (mm) | Hole Ø (in) | Nearest drill | Edge distance |
|---|
Example data
Use these examples to test the calculator. Click a row to load its values into the form.
| Units | Bolt size | Fit | Plating (µm) | Extra allowance |
|---|---|---|---|---|
| Metric | M8 | Normal | 15 | 0.2 mm |
| Imperial | 1/2" | Normal | 10 | 0.005 in |
| Metric | M12 | Loose | 0 | 0 mm |
Formulas used
- BaseHole is taken from standards-inspired lookup or fallback rules for the selected fit class.
- Plating adds twice the thickness to diameter: Δplating = 2 × t (converted to the current units).
- Extra fabrication allowance is added directly to hole diameter.
- Final hole: Hole = BaseHole + Δplating + ExtraAllowance.
- Nearest drill is chosen from a curated list of common sizes for the unit system.
- Recommended minimum edge distance ≈ factor × Hole.
Recommended clearance table (metric)
Typical recommended clearance hole diameters (mm) for common metric bolts by fit class.
| Bolt | Close fit Ø (mm) | Normal fit Ø (mm) | Loose fit Ø (mm) |
|---|---|---|---|
| M6 | 6.6 | 7.0 | 8.0 |
| M8 | 9.0 | 10.0 | 11.0 |
| M10 | 11.0 | 12.0 | 13.0 |
| M12 | 13.5 | 14.0 | 15.0 |
| M16 | 17.5 | 18.0 | 19.0 |
| M20 | 22.0 | 24.0 | 26.0 |
Recommended clearance table (imperial)
Typical recommended clearance hole diameters (inch) for common bolt sizes by fit class.
| Bolt | Close fit Ø (in) | Normal fit Ø (in) | Loose fit Ø (in) |
|---|---|---|---|
| 1/4" | 0.2813 | 0.3125 | 0.3438 |
| 5/16" | 0.3438 | 0.3750 | 0.4063 |
| 3/8" | 0.4063 | 0.4375 | 0.4688 |
| 1/2" | 0.5313 | 0.5625 | 0.5938 |
| 5/8" | 0.6563 | 0.6875 | 0.7188 |
| 3/4" | 0.8125 | 0.8750 | 0.9375 |
How to use this calculator
- Select units, bolt size, and fit class.
- Optionally enter plating thickness and extra fabrication allowance.
- Click Calculate to see hole size, drill suggestion, and edge distance.
- Click Add to table to capture a row for exporting or comparison.
- Use Download CSV or Download PDF to export the batch table.
This tool supports common sizes and recommendations. Always verify with your project standards, drawings, and fabrication practices before production.
FAQs
What is a clearance hole?
A clearance hole is drilled larger than the bolt’s shank so the bolt passes freely. It allows easy assembly, tolerance for misalignment, and space for coatings without thread interference or binding during installation.
How do close, normal, and loose fits differ?
Close fit minimizes play for accurate location. Normal fit balances alignment and ease of assembly for general work. Loose fit provides extra clearance for field tolerances, thicker coatings, burrs, or slotted connections requiring larger positional freedom.
How does plating thickness affect hole size?
Coatings add thickness all around the bolt, increasing effective diameter. This tool adds twice the plating thickness to the recommended hole, compensating for coating on both sides so the bolt still passes freely after finishing.
Which drill size should I select?
After calculation, use the suggested nearest drill size for your unit system. When specifications dictate exact sizes, follow the drawing. If in doubt, choose the next larger drill and confirm fit on representative parts.
Is this suitable for stainless or aluminum parts?
Yes. The clearance concept is material independent. However, drilling behavior and burr formation vary by material. Deburr holes, consider thermal expansion in service, and verify galvanic compatibility when mixing fasteners and base materials.
What edge distance should I use from the hole center?
As a starting rule, at least 1.5× to 2.0× the final hole diameter. This tool reports a minimum based on your chosen factor. Always check project codes, detailing standards, and engineer instructions before fabrication.