Screw Tap Drill Chart for Threaded Holes
This screw drill size chart provides recommended drill bit sizes for metal cutting taps, helping ensure proper fit, thread engagement, and reliable fastening in a variety of applications.
Use the chart below to find the correct drill size for common screw sizes.
| Drill Bit Size Category | Drill Bit Size | Decimal Inch Size | Metric mm Size | Tap or Screw Size | Tap Or Screw Size Category | Thread Standard |
|---|---|---|---|---|---|---|
| Inch | 3/64 | 0.0469 | 1.19 | 0-80 | Screw | Fine |
| Number | 53 | 0.0595 | 1.51 | 1-64 | Screw | Coarse |
| Number | 53 | 0.0595 | 1.51 | 1-72 | Screw | Fine |
| Number | 51 | 0.0670 | 1.70 | 2-56 | Screw | Coarse |
| Number | 50 | 0.0700 | 1.78 | 2-64 | Screw | Fine |
| Number | 47 | 0.0785 | 1.99 | 3-48 | Screw | Coarse |
| Number | 45 | 0.0820 | 2.08 | 3-56 | Screw | Fine |
| Number | 43 | 0.0890 | 2.26 | 4-40 | Screw | Coarse |
| Number | 42 | 0.0935 | 2.37 | 4-48 | Screw | Fine |
| Number | 38 | 0.1015 | 2.58 | 5-40 | Screw | Coarse |
| Number | 37 | 0.1040 | 2.64 | 5-44 | Screw | Fine |
| Number | 36 | 0.1065 | 2.71 | 6-32 | Screw | Coarse |
| Number | 33 | 0.1130 | 2.87 | 6-40 | Screw | Fine |
| Number | 29 |
0.1360 |
3.45 | 8-32 | Screw | Coarse |
| Number | 29 | 0.1360 | 3.45 | 8-36 | Screw | Fine |
| Number | 25 | 0.1495 | 3.80 |
10-24 |
Screw | Coarse |
| Number | 21 | 0.1590 | 4.04 | 10-32 | Screw | Fine |
| Number | 16 | 0.1770 | 4.50 | 12-24 | Screw | Coarse |
| Number | 14 | 0.1820 | 4.62 | 12-28 | Screw | Fine |
Understanding Screw Drill Sizes for Threaded Holes
When working with screws in metal or other rigid materials, drill sizes are used to prepare a hole for tapping rather than simply creating a pilot hole. These drill sizes are known as tap drill sizes and are selected to produce the correct percentage of thread engagement for a secure and reliable fit.
In most machining and fabrication applications, a tap drill size is chosen to achieve approximately 70–75% thread engagement. This provides a balance between strength and ease of tapping while minimizing tool wear and breakage. For example, an 8-32 screw typically uses a #29 drill size when tapping threads in metal.
Tap Drill Sizes vs Pilot Holes
There is often confusion between tap drill sizes and pilot holes, but they serve different purposes. Tap drill sizes are used when cutting internal threads with a tap, typically in materials such as steel, aluminum, or other metals. Pilot holes, on the other hand, are used for self-tapping screws or wood screws in softer materials such as wood, plastic, or sheet metal. These holes are intended to guide the screw and reduce material splitting, not to create precise internal threads.
The key difference is that pilot holes are used for thread forming, while tap drill sizes are used for thread cutting. This distinction is important when selecting the correct drill size for the application.
How to Use a Screw Tap Drill Chart
This chart is used when preparing threaded holes in metal using a tap.
- Identify the screw or fastener size and thread specification.
- Locate the corresponding tap drill size in the chart.
- Drill the hole to the recommended size.
- Use a tap to cut internal threads before installing the fastener.
Why Thread Engagement Matters
Proper thread engagement is critical for fastener performance. A hole that is too small increases tapping torque and the risk of tool breakage, while a hole that is too large reduces thread strength and holding capability.
Standard tap drill sizes are designed to provide optimal engagement for most applications, ensuring consistent and reliable threaded connections.
Applications for Tap Drill Sizes
Tap drill sizes are commonly used in machining, fabrication, maintenance, and repair operations where threaded holes are required in metal components. These applications require precision and consistency that pilot holes alone cannot provide.
Printable Screw Tap Drill Chart
Download a printable PDF version of this chart for convenient reference when selecting tap drill sizes for threaded holes.
Related Drill and Tap Charts
Frequently Asked Questions
What is the difference between a tap drill size and a pilot hole?
A tap drill size is used to prepare a hole for cutting internal threads with a tap, typically in metal. A pilot hole is used for guiding screws in softer materials like wood or plastic where the screw is designed to form the thread as it is inserted.
Do screws require tap drill sizes?
Yes, when screws or fasteners are used in metal or other hard materials, a tap drill size is required to create internal threads before installation. This ensures proper thread engagement and holding strength.
Are pilot hole sizes standardized like tap drill charts?
No. Pilot hole sizes vary depending on the material and type of screw being used. Unlike tap drill sizes, they are not typically defined by standardized charts.
What percentage of thread engagement do tap drill sizes provide?
Most standard tap drill sizes are designed to provide approximately 70–75% thread engagement, which offers a good balance between strength and ease of tapping.
When should I use a pilot hole instead of tapping?
Use a pilot hole when installing self-tapping screws or working with softer materials like wood, plastic, or sheet metal. Use tap drill sizes when creating threaded holes in harder materials.
