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UNEF Thread Pitch Chart
This UNEF Thread Chart provides a quick reference for Unified National Extra Fine thread sizes and is designed for engineers, machinists, maintenance technicians, manufacturers, apprentices and workshop professionals. Whether you're selecting taps, dies or drill bits, this chart helps you identify the exact specifications needed for precision threading work.
| Diameter | TPI | Drill Size (mm) |
|---|---|---|
| No. 12 | 32 | 4.7 mm |
| 1/4" | 32 | 5.5 mm |
| 5/16" | 32 | 7.1 mm |
| 3/8" | 32 | 8.6 mm |
| 7/16" | 28 | 10.1 mm |
| 1/2" | 28 | 11.7 mm |
| 9/16" | 24 | 13.0 mm |
| 5/8" | 24 | 14.75 mm |
| 11/16" | 24 | 16.25 mm |
| 3/4" | 20 | 17.5 mm |
| 13/16" | 20 | 19.25 mm |
| 7/8" | 20 | 20.75 mm |
| 15/16" | 20 | 22.25 mm |
| 1" | 20 | 23.75 mm |
| 1-1/8" | 18 | 26.75 mm |
| 1-1/4" | 18 | 30.0 mm |
| 1-3/8" | 18 | 33.0 mm |
| 1-1/2" | 18 | 36.0 mm |
What is a UNEF Thread?
UNEF stands for Unified National Extra Fine, a thread standard engineered for precision and reliability. As part of the Unified Thread Standard (UTS), UNEF uses a 60° thread profile that delivers superior performance in demanding applications.
Extra fine threads provide greater clamping force and precise adjustment, making them ideal where maximum thread engagement is required in a limited space. UNEF threads are commonly used in aerospace, automotive, precision engineering, hydraulics and instrumentation—industries where accuracy and holding power are critical to safety and performance.
How to Read the UNEF Thread Chart
The UNEF Thread Chart above displays the essential specifications for accurate thread selection and machining:
- Nominal Thread Size – The thread diameter, shown in fractional inches.
- Threads Per Inch (TPI) – The number of threads within one inch of length. Higher TPI indicates finer pitch and closer thread spacing.
- Tap Drill Size (mm) – The recommended drill diameter in millimetres for creating the correct hole before tapping.
Use these dimensions to select the correct UNEF taps and dies for your project. Matching the drill size to the thread specification ensures proper thread depth, strength and performance.
Common Applications
UNEF threads are trusted across industries where precision and reliability cannot be compromised:
- Aerospace and aircraft assembly
- Automotive engineering and engine components
- Hydraulic equipment and fluid power systems
- Precision machinery and machine tools
- Instrumentation and measurement devices
- Manufacturing and industrial equipment
- High-performance mechanical assemblies
When your application demands fine thread pitch, superior clamping force and precise adjustment, UNEF threads deliver the performance and reliability you need.
Frequently Asked Questions
What does UNEF stand for?
UNEF stands for Unified National Extra Fine. It is a thread standard within the Unified Thread Standard (UTS) that provides finer pitch than both UNC (coarse) and UNF (fine) threads.
What is the difference between UNC, UNF and UNEF?
UNC (Unified National Coarse) has the largest pitch and is used for general-purpose fastening and rapid assembly. UNF (Unified National Fine) offers finer pitch for improved clamping force and vibration resistance. UNEF (Unified National Extra Fine) provides the finest pitch, ideal for precision applications, limited thread engagement and situations requiring maximum holding power in a compact space.
When should I choose UNEF threads?
Choose UNEF threads when you need maximum clamping force in a limited space, require precise adjustment, or are working with materials that benefit from finer pitch. UNEF is ideal for aerospace, automotive and precision engineering applications where performance and reliability are essential.
Are UNEF threads compatible with metric threads?
No. UNEF threads follow the Unified Thread Standard (UTS) with a 60° thread angle and are measured in inches. Metric threads use a different pitch system and thread angle. Always verify thread specifications before assembly to ensure compatibility.