Clearance Hole Calculator
Calculate the clearance hole diameter required for a bolt or screw. Toggle units, choose fit class, and consult ASME-style reference tables.
A clearance hole is a hole drilled in a material that is slightly larger than the bolt or screw diameter, allowing it to pass through freely. The correct clearance hole size ensures proper assembly while accounting for manufacturing tolerances and thermal expansion.
Clearance Hole Formula
CH = (D + DH) / 2
Where:
- CH = Clearance Hole Diameter
- D = Fastener Diameter
- DH = Fastener Head Diameter
Try an example:
ASME Reference Tables
| Nominal Size | Close Fit | Normal Fit | Loose Fit | Recommended Drill |
|---|
Frequently Asked Questions
What’s the difference between clearance holes and tap holes?
Clearance holes are larger than the fastener to allow it to pass through, while tap holes are smaller and threaded to accept the fastener directly into the material.
What are the different fit classes?
Close fit provides minimal clearance for precision applications, normal fit is for general use, and loose fit allows for misalignment or thermal expansion.
Should I use metric or imperial units?
Use the unit system that matches your fasteners. Metric is common worldwide, while imperial is still used in the US. This calculator supports both.
How do I use this calculator?
Enter your fastener diameter and head diameter, select your preferred fit class, and the calculator will instantly show the recommended clearance hole size.
Recommended clearance hole (CH)
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