Enter your Fastener Diameter, choose a Fit Class (close, normal, or loose), and add your Material Thickness to find the right Clearance Hole Diameter for your application — along with the Total Clearance and the exact Recommended Drill Bit size to grab off the shelf.
Clearance Hole Diameter
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Total Clearance
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Recommended Drill Bit
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A clearance hole is a hole that allows a fastener to pass through without the threads engaging the material. It provides enough space for easy insertion while maintaining proper alignment.
The clearance hole diameter is calculated by adding the fastener diameter to the appropriate clearance amount based on the fit class. Normal fit provides standard clearance, close fit minimizes gaps, and loose fit allows for misalignment.
Normal fit provides standard clearance for general applications. Close fit minimizes clearance for precision assemblies. Loose fit provides extra clearance to accommodate misalignment or thermal expansion.
For an M8 bolt, the clearance hole diameter is typically 9mm for normal fit, 8.5mm for close fit, and 10mm for loose fit, depending on the application requirements.
Material thickness doesn't directly affect the hole diameter but influences drill bit selection and drilling technique. Thicker materials may require stepped drilling or specialized bits.
Use a drill bit that matches the calculated clearance hole diameter. For best results, choose the closest standard drill bit size that meets or slightly exceeds the calculated diameter.
This calculator works with any unit system. Simply enter the fastener diameter in your preferred units (mm or inches) and the results will be in the same units.
A hole that's too small will prevent proper fastener insertion or cause thread damage. A hole that's too large reduces clamping effectiveness and may allow excessive movement or misalignment.