2025 Comprehensive Guide to Imperial Thread Drill Sizes (UNC and UNF)
When working with imperial threads, choosing the correct drill bit size is crucial for precise threading and secure fastening. This guide provides a detailed table of drill sizes for both Unified National Coarse (UNC) and Unified National Fine (UNF) threads, along with useful tips to ensure accurate results.
Drill Sizes Suitable for a 13mm Hole
For a 13mm hole, you can use the following drill bit sizes depending on the threading requirements:
- 1/2"-13 UNC: Requires a drill size of 27/64" (10.72mm).
- 1/2"-20 UNF: Requires a drill size of 29/64" (11.51mm).
Ensure you select the appropriate size based on whether you’re working with coarse (UNC) or fine (UNF) threads.
What Are UNC and UNF Threads?
-
UNC (Unified National Coarse): These threads have a coarser pitch and are better suited for softer materials like aluminum, wood, and plastics. They are widely used in general mechanical applications where strength and durability are required.
-
UNF (Unified National Fine): These threads have a finer pitch, offering better grip and strength in harder materials. They are commonly used in precision applications like automotive and aerospace industries.
Drill Size Chart for UNC Threads
| **Thread Size (UNC) ** | **Threads per Inch (TPI) ** | **Drill Size (Inches) ** | **Drill Size (Millimeters) ** | **Applications ** |
|---|---|---|---|---|
| #1-64 UNC | 64 | 3/64" | 1.19 | Precision assemblies |
| #2-56 UNC | 56 | 5/64" | 1.98 | Electronics and small parts |
| #4-40 UNC | 40 | 3/32" | 2.38 | Light-duty assemblies |
| #6-32 UNC | 32 | 7/64" | 2.78 | Common in electronics |
| #8-32 UNC | 32 | 9/64" | 3.57 | Widely used in mechanics |
| #10-24 UNC | 24 | 5/32" | 3.97 | Standard mechanical uses |
| 1/4"-20 UNC | 20 | 13/64" | 5.16 | General-purpose threading |
| 5/16"-18 UNC | 18 | F (0.257") | 6.53 | Heavy-duty applications |
| 3/8"-16 UNC | 16 | 5/16" | 7.94 | Structural connections |
| 1/2"-13 UNC | 13 | 27/64" | 10.72 | Industrial use |
Drill Size Chart for UNF Threads
| **Thread Size (UNF) ** | **Threads per Inch (TPI) ** | **Drill Size (Inches) ** | **Drill Size (Millimeters) ** | **Applications ** |
|---|---|---|---|---|
| #1-72 UNF | 72 | 3/64" | 1.19 | Precision engineering |
| #2-64 UNF | 64 | 5/64" | 1.98 | Small electronic devices |
| #4-48 UNF | 48 | 3/32" | 2.38 | Light-duty assemblies |
| #6-40 UNF | 40 | 7/64" | 2.78 | Medium-duty connections |
| #8-36 UNF | 36 | 9/64" | 3.57 | Precision assemblies |
| #10-32 UNF | 32 | 7/64" | 2.78 | Automotive fasteners |
| 1/4"-28 UNF | 28 | 7/32" | 5.56 | High-precision uses |
| 5/16"-24 UNF | 24 | L (0.290") | 7.37 | Secure mechanical connections |
| 3/8"-24 UNF | 24 | Q (0.332") | 8.43 | Heavy-duty precision work |
| 1/2"-20 UNF | 20 | 29/64" | 11.51 | Industrial applications |
Tips for Choosing the Right Drill Size
- Match the Thread Specification: Always refer to the thread size and TPI (threads per inch) to determine the correct drill size.
- Use a Drill Size Chart: Keep a drill size chart handy to ensure accuracy during your work.
- Consider Material Properties: For softer materials, slightly smaller drill sizes may provide better thread engagement. For harder materials, use precise sizes to avoid over-tightening or stripping threads.
- Lubrication: Apply cutting oil during drilling and threading to reduce friction and prolong tool life.
- Test Fits: Before final assembly, test the threaded components to ensure a proper fit.
Final Thoughts
Using the correct drill size for imperial threads ensures strong and secure connections in your projects. Whether working with UNC or UNF threads, this guide provides the essential information you need to succeed. For precise results, always double-check specifications and follow industry best practices.
Got questions or additional thread sizes to add? Let us know in the comments below!
