The standard tap drill size chart is a guide that provides the recommended tap and clearance drill sizes for various types of materials and desired thread counts. This chart is especially useful for machinists and engineers who need to accurately determine the correct drill size for their project.
Standard Tap Drill Size Table
Here is a table on tap drill sizes for reference.
| Material Type | Threads per Inch (TPI) | Thread Drill Size | Tap Drill Size |
| Mild Steel | 0-80 | #56 | #60 |
| Mild Steel | 8-32 | #34 | #36 |
| Mild Steel | 10-24 | #29 | #30 |
| Mild Steel | ¼”-20 | #14 | #15 |
| Mild Steel | 5/16”-18 | 7/32” (#8) | 3/16” (#7) |
| Stainless Steel | 0-80 | F#56 | F#60 |
| Stainless Steel | 8-32 | F#34 | F#36 |
| Stainless Steel | 10-24 | F#29 | F#30 |
| Stainless Steel | ¼”-20 | F#14 | F#15 |
| Stainless Steel | 5/16”-18 | 7/32” (#8) | 3/16” (#7) |
How to Use the Standard Tap Drill Size Chart
- Select the material type. The material type will determine the size of the clearance hole it requires. If a hole is drilled in something thicker than the material type’s recommended size, it will be too tight and require reaming afterward.
- Determine the desired size of thread you want to create in the material. This is measured by thread count or the number of threads per inch (TPI).
- Check the chart to find a thread drill size that is closest to your desired TPI. For example, if you wanted 8 TPI, then you would select a #34 drill bit as this creates an 8TPI thread in most materials.
- Pick a tap drill size based on your selected thread drill size from step 3 and the material’s thickness from step 1. For example, if you chose a #34 drill bit for 8 TPI and are working with 1/4″ thick material, then you would use a 7/32″ tap drill (#8).
- Use your tap drill bit to create the threads in your workpiece by rotating it clockwise until it stops (first) and then counterclockwise until it stops twice more (second and third). Make sure to use cutting oil while drilling so as not to overheat or damage your tools!
- Remove the tap drill bit and you’re ready to use your newly created threads!
What Size Drill Do I Need For A Tap?
The drill size you need for a tap is determined by the material type [1], desired thread count, and thickness of the material. To accurately determine what size drill bit you should use, refer to a standard tap drill size chart for your specific material.
What Size Hole Do I Drill for a 1-2-inch Tap?
For a 1/2-inch tap, you would need to use a 29/64-inch drill bit for most materials. Refer to a standard tap drill size chart for your specific material for more accurate sizing information.
What Size Tap Do I Need for a 3 8 Hole?
For a 3/8 hole, you would need to use a 21/64-inch drill bit for most materials. Refer to a standard tap drill size chart for your specific material for more accurate sizing information.
What Size Drill for a 10mm Tap?
For a 10mm tap, you would need to use a 12.5mm (1/2 inch) drill bit for most materials. Refer to a standard tap drill size chart for your specific material for more accurate sizing information.
Conclusion
Using the standard tap drill size chart can ensure you select the right-sized drill bit and tap for the job. Knowing what size drill you need for a tap is essential to create the desired thread count in your material. This chart provides easy and accurate information to help you determine what size drill and tap are required for your project.