Borrowing a bit from our friends at Bolt Depot, their chart showing US Machine Screw Diameters is helpful, but often I’m designing with Metric units (or a unit-less system that outputs in millimeters) and I need to convert Imperial units to mm. (I tend to do a lot of work using OpenSCAD and Inkscape for 3D printing.)
The chart below allows me to specify screws and bolts and then design holes that will work. For instance, I used a lot of #4 screws, and the chart tells me I need a hole diameter of approximately 2.794mm. Handy!
| Size | Thread Diameter | ||
|---|---|---|---|
| Decimal | Nearest Fractional | Metric | |
| #0 | 0.06″ | 1/16″ | 1.524mm |
| #1 | 0.07″ | 5/64″ | 1.778mm |
| #2 | 0.08″ | 3/32″ | 2.032mm |
| #3 | 0.09″ | 7/64″ | 2.286mm |
| #4 | 0.11″ | 7/64″ | 2.794mm |
| #5 | 0.12″ | 1/8″ | 3.048mm |
| #6 | 0.13″ | 9/64″ | 3.302mm |
| #8 | 0.16″ | 5/32″ | 4.046mm |
| #10 | 0.19″ | 3/16″ | 4.826mm |
| #12 | 0.21″ | 7/32″ | 5.334mm |
| #14 | 0.24″ | 1/4″ | 6.096mm |
See Also: Millimeters, Inches, Fraction, Decimals