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Quickly find the correct drill bit size for pilot holes, tap drills, clearance holes, and countersinks. Support for fractional, number, letter, and metric drill sizes.
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Common in the US, ranging from 1/64" to 1/2" and larger. Most commonly used for general purpose drilling in wood, metal, and plastic.
Numbered from #80 (smallest) to #1 (largest). Used primarily for precision work and tapping holes.
Lettered A through Z, with A being smallest. Commonly used for tapping and precision work.
Sizes in millimeters, standard outside the US. Precise sizing for metric fasteners and specifications.
| Fraction | Decimal | Millimeters |
|---|---|---|
| 1/64 | 0.0156" | 0.40mm |
| 1/32 | 0.0313" | 0.79mm |
| 3/64 | 0.0469" | 1.19mm |
| 1/16 | 0.0625" | 1.59mm |
| 5/64 | 0.0781" | 1.98mm |
| 3/32 | 0.0938" | 2.38mm |
| 7/64 | 0.1094" | 2.78mm |
| 1/8 | 0.1250" | 3.17mm |
| 9/64 | 0.1406" | 3.57mm |
| 5/32 | 0.1563" | 3.97mm |
| 11/64 | 0.1719" | 4.37mm |
| 3/16 | 0.1875" | 4.76mm |
| 13/64 | 0.2031" | 5.16mm |
| 7/32 | 0.2188" | 5.56mm |
| 15/64 | 0.2344" | 5.95mm |
| 1/4 | 0.2500" | 6.35mm |
| 17/64 | 0.2656" | 6.75mm |
| 9/32 | 0.2813" | 7.14mm |
| 19/64 | 0.2969" | 7.54mm |
| 5/16 | 0.3125" | 7.94mm |
| 21/64 | 0.3281" | 8.33mm |
| 11/32 | 0.3438" | 8.73mm |
| 23/64 | 0.3594" | 9.13mm |
| 3/8 | 0.3750" | 9.53mm |
| 25/64 | 0.3906" | 9.92mm |
| 13/32 | 0.4063" | 10.32mm |
| 27/64 | 0.4219" | 10.72mm |
| 7/16 | 0.4375" | 11.11mm |
| 29/64 | 0.4531" | 11.51mm |
| 15/32 | 0.4688" | 11.91mm |
| 31/64 | 0.4844" | 12.30mm |
| 1/2 | 0.5000" | 12.70mm |
A pilot hole is small and guides the screw, reducing splitting and drift. A clearance hole is larger, allowing the screw to pass through freely without binding.
A tap drill is the correct size hole to drill before threading. It allows about 75% of the thread to form, creating strong threads without excessive stress.
A clearance hole is typically 10-15% larger than the screw's major diameter, allowing the screw to pass freely without friction.
Countersinking creates a conical depression to allow screw heads to sit flush with the surface. It's done for flush finishing, appearance, and to prevent catching.
Wood fibers compress and grip better, so pilots can be smaller. Metal needs larger pilots to reduce thread stripping and binding.
These are alternative sizing systems. Letter drills (A-Z) and number drills (#1-#80) provide precise diameters, especially useful for tapping and metric work.
Slightly larger is usually better than smaller (more room for screws to slide). Smaller risks binding. Always stay within 10% of recommended size.
Fractional bits (1/64" to 1/2") are most versatile and affordable. For precision work, letter or number bits offer better consistency.
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