Bolt Hole Inputs
Calculation History
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| Date | Bolt | Hole type | Final diameter |
|---|---|---|---|
| No saved calculations yet. | |||
Formula Used
Tap drill: bolt diameter minus thread pitch. Engagement adjustment scales the removed thread depth. Final sizing still needs shop verification.
Countersink depth: (top diameter − hole diameter) ÷ [2 × tan(angle ÷ 2)]. The calculation assumes a centred conical recess. Verify actual fastener geometry before machining.
Removed volume: hole area multiplied by material thickness. Counterbores and countersinks add their extra recess volumes. Density converts that volume into estimated mass.
Clearance lookups use common ISO-style reference values. Custom standards can override the calculated diameter. Engineering approval remains necessary for critical assemblies.
How To Use
- Select the metric bolt diameter and hole type.
- Choose fit, thread, head, and material settings.
- Enter plate thickness, tolerances, and layout dimensions.
- Submit the form and review every warning.
- Export results for workshop or inspection records.
Example Data
| Example | Bolt | Hole | Material | Purpose |
|---|---|---|---|---|
| General bracket | M8 × 1.25 | Normal clearance | Mild steel | Standard assembly clearance |
| Threaded plate | M10 × 1.50 | 75% tapped | Aluminium | Internal thread preparation |
| Recessed cap screw | M6 × 1.00 | Counterbore | Stainless steel | Flush socket-head installation |
| Flat-head screw | M5 × 0.80 | 90° countersink | Brass | Flush surface finish |
Metric Reference Tables
Common Coarse Threads
| Bolt | Pitch | Basic tap drill |
|---|---|---|
| M3 | 0.50 mm | 2.50 mm |
| M4 | 0.70 mm | 3.30 mm |
| M5 | 0.80 mm | 4.20 mm |
| M6 | 1.00 mm | 5.00 mm |
| M8 | 1.25 mm | 6.75 mm |
| M10 | 1.50 mm | 8.50 mm |
| M12 | 1.75 mm | 10.25 mm |
| M16 | 2.00 mm | 14.00 mm |
| M20 | 2.50 mm | 17.50 mm |
| M24 | 3.00 mm | 21.00 mm |
Common Clearance References
| Bolt | Close | Normal | Loose |
|---|---|---|---|
| M3 | 3.7 | 3.9 | 4.2 |
| M4 | 4.3 | 4.5 | 4.8 |
| M5 | 5.3 | 5.5 | 5.8 |
| M6 | 6.4 | 6.6 | 7.0 |
| M8 | 8.4 | 9.0 | 10.0 |
| M10 | 10.5 | 11.0 | 12.0 |
| M12 | 13.0 | 14.0 | 15.0 |
| M16 | 17.0 | 18.0 | 19.0 |
| M20 | 21.0 | 22.0 | 24.0 |
| M24 | 25.0 | 26.0 | 28.0 |
Common Fine Threads
| Bolt | Fine pitch | Basic tap drill |
|---|---|---|
| M6 | 0.75 mm | 5.25 mm |
| M8 | 1.00 mm | 7.00 mm |
| M10 | 1.25 mm | 8.75 mm |
| M12 | 1.50 mm | 10.50 mm |
| M16 | 1.50 mm | 14.50 mm |
| M20 | 2.00 mm | 18.00 mm |
| M24 | 2.00 mm | 22.00 mm |
Head Planning References
| Head type | Diameter estimate | Height estimate |
|---|---|---|
| Socket head | 1.50 × bolt diameter | 1.00 × bolt diameter |
| Hex head | 1.60 × bolt diameter | 0.65 × bolt diameter |
| Button head | 1.80 × bolt diameter | 0.55 × bolt diameter |
| Countersunk head | 2.00 × bolt diameter | 0.50 × bolt diameter |
These proportions are planning estimates. Enter measured or standard-specific head dimensions for production.
Common Metric Drill Sizes
| Range | Common increments | Typical use |
|---|---|---|
| 0.5–3.0 mm | 0.1 mm | Small screws and pilot holes |
| 3.0–10.0 mm | 0.1 or 0.5 mm | General metric fasteners |
| 10.0–20.0 mm | 0.5 mm | Large clearance and tapping |
| 20.0–50.0 mm | 0.5 or 1.0 mm | Annular cutters and large drills |
| 50.0–100.0 mm | 1.0 mm or custom | Boring and specialised tooling |
Frequently Asked Questions
What is a metric clearance hole?
It is larger than the bolt diameter. The gap supports assembly and alignment. Fit selection controls the available movement.
How is a tap drill estimated?
Subtract thread pitch from nominal bolt diameter. This approximates common seventy-five-percent engagement. Always verify the chosen tap chart.
Which clearance fit should I choose?
Close fits support accurate alignment. Normal fits suit general workshop assembly. Loose fits help difficult field installation.
Does coating change the hole size?
Yes, coating increases the effective bolt diameter. This calculator adds twice radial coating thickness. Confirm the coating’s final measured build.
How is countersink depth calculated?
The calculator uses cone geometry. It compares opening and pilot diameters. The selected included angle controls depth.
Why are spacing warnings included?
Small spacing may weaken the plate. Edge distance also affects tear-out resistance. Treat warnings as early design screening.
Are spindle speeds guaranteed?
No, they are starting estimates. Tool material and coolant change performance. Follow machine and drill manufacturer guidance.
Can I calculate circular bolt patterns?
Yes, choose the circular pattern option. Enter the bolt-circle diameter and count. Coordinates are generated around the plate centre.
Can these results replace engineering approval?
No, they support planning only. Critical joints require standards and professional review. Verify tolerances before releasing production drawings.