Formula used
The calculator begins with the selected reference hole. It then adds process and user allowances. Finally, it applies the entered hole tolerance.
Thread pitch is shown for identification and shop communication. Clearance diameter usually follows the fastener major diameter. Always verify unusual hardware before machining.
How to use the calculator
- Select inches or millimetres before entering dimensions.
- Choose the thread, fit class, and reference method.
- Enter measured fastener size and relevant tolerances.
- Select the manufacturing process and add allowances carefully.
- Choose a preferred drill family and rounding rule.
- Submit the form and review warnings before fabrication.
- Copy, print, or export the result for shop use.
Worked example data
Choose an example to load its values into the form.
| Example | Fit or method | Typical target | Purpose |
|---|---|---|---|
| 5/16-18 bolt | Close fit | About 0.328 in | Controlled alignment with accurate positioning |
| 5/16-24 screw | Normal fit | About 0.344 in | General machinery and routine assembly |
| Fabricated bracket | Loose fit | About 0.359 to 0.375 in | Easier assembly and positional accommodation |
| Custom design | 0.020 in clearance | 0.3325 in before allowances | Design-specific clearance requirement |
| Existing 11/32 hole | Acceptance check | 0.34375 in | Verify a measured or planned hole |
Frequently asked questions
What is the nominal diameter of a 5/16 fastener?
Its nominal major diameter is 0.3125 inches. That equals 7.9375 millimetres. Actual hardware dimensions can vary slightly.
What is a normal clearance hole for 5/16 hardware?
A common normal-fit target is near 0.344 inches. An 11/32-inch drill equals 0.34375 inches. Confirm the governing drawing before drilling.
What is a close-fit clearance hole?
A close fit minimises free movement around the fastener. It needs accurate hole location. Reaming may improve dimensional control.
Why can loose-fit recommendations differ?
Different charts target different assembly conditions. Some use approximately 23/64 inch. Others recommend 3/8 inch for field work.
Does thread pitch change the clearance hole?
Usually, clearance follows the fastener major diameter. Pitch mainly identifies the threaded fastener. Special hardware can require different treatment.
Is a clearance hole the same as a tap-drill hole?
No. A clearance hole lets the fastener pass through. A tap-drill hole is smaller and receives internal threads.
Should the drill always round upward?
Rounding upward helps avoid an undersized clearance hole. Precision work may use closer tooling. Project tolerances should control the choice.
How are coating allowances treated?
This calculator adds entered coating allowance diametrically. Enter zero when finishing already enlarges the hole. Verify the final coated dimension.
Can I verify an existing hole?
Yes. Enter the measured diameter in the existing-hole field. The result compares it with minimum and maximum limits.
Are the results suitable for structural joints?
The calculator provides dimensional guidance only. Structural joints may have specific code requirements. Obtain engineering approval where required.
Why include manufacturing process allowances?
Some processes produce larger variation or taper. Allowances help model practical fabrication needs. Measure critical finished holes before assembly.