Screw Machine Tap Size Chart
Use this screw machine tap size chart to look up the nominal diameter of numbered screw sizes, from #0 through #12, and their nearest common fractional-inch equivalents. These are screw size diameters, not recommended tap-drill hole sizes. For hole preparation, consult a tap drill chart for the specific thread pitch.
Screw Machine Tap Size and Diameter Chart
| Screw Size | Nominal Diameter (Decimal Inches) | Nearest Fraction (Inches) |
|---|---|---|
| #0 | 0.060" | 1/16" |
| #1 | 0.073" | 5/64" |
| #2 | 0.086" | 3/32" |
| #3 | 0.099" | 7/64" |
| #4 | 0.112" | 7/64" |
| #5 | 0.125" | 1/8" |
| #6 | 0.138" | 9/64" |
| #8 | 0.164" | 5/32" |
| #10 | 0.190" | 3/16" |
| #12 | 0.216" | 7/32" |
How to Use This Chart
Find the numbered screw size in the first column, then read its nominal diameter in decimal inches and the closest common fractional-inch size. The fractional value is an approximation and should not be substituted for an exact machining tolerance or tap drill specification.
Frequently Asked Questions
What does a #10 screw size mean?
A #10 screw has a nominal major diameter of 0.190 inch. Its closest common fractional-inch equivalent in this chart is 3/16 inch.
Is the nearest fraction an exact conversion?
No. It is the closest common fractional-inch size, not necessarily the exact nominal diameter.
Does this chart show which drill bit to use before tapping?
No. Tap drill selection also depends on thread pitch and the desired thread engagement. Use a dedicated tap drill chart for that purpose.
What is the nominal diameter of a #6 screw?
A #6 screw has a nominal diameter of 0.138 inch; its nearest fraction in this chart is 9/64 inch.
Why are #3 and #4 both listed near 7/64 inch?
Their nominal diameters differ (0.099 inch and 0.112 inch), but the original chart assigns 7/64 inch as the nearest common fraction for both.