Convert any drill bit size instantly with our detailed size charts. From fractional inches to millimeters, letter sizes to number sizes - get all the measurements you need for perfect holes every time. Free printable reference guides included.
| Fractional Inches | Decimal Inches | Millimeters | Closest Letter Size |
|---|---|---|---|
| 1/16" | 0.0625" | 1.5875 mm | - |
| 1/8" | 0.125" | 3.175 mm | - |
| 1/4" | 0.250" | 6.35 mm | F |
Cutting speed (CS) is measured in Surface Feet per Minute (SFM) and is calculated using:
CS = (p × D × RPM) / 12
Where:
| Material | SFM Range | Notes |
|---|---|---|
| Mild Steel | 60-100 | Use lower range for harder steels |
| Aluminum | 200-300 | Higher speeds possible with cooling |
| Screw Size | Drill Size | Decimal Equivalent |
|---|---|---|
| #4-40 | #43 | 0.089" |
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