3/8-24 UNF Thread Quick Specifications
| Parameter | Specification | |
| Thread Standard | Unified Thread Standard (UTS) | |
| Thread Series | UNF | |
| Nominal Size | 3/8 | |
| Thread Designation | 3/8-24 UNF | |
| Threads Per Inch (TPI) | 24 | |
| Major Diameter | 0.3750 in | 9.525 mm |
| Pitch | 0.0417 in | 1.059 mm |
| Pitch Diameter | 0.3479 in | 8.837 mm |
| Minor Diameter | 0.3254 in | 8.265 mm |
| Thread Height | 0.0226 in | 0.574 mm |
| Addendum | 0.0135 in | 0.343 mm |
| Thread Angle | 60° | |
| Common Classes | 2A / 2B | |
| Typical Use | Precision electronic assemblies | |
Introduction
The 3/8-24 UNF thread is a Unified National Fine (UNF) thread, which is primarily used in North America and widely adopted internationally in industrial and electronic applications. Unified threads are identified using an inch-based numbering system.
The 3/8-24 UNF thread has a nominal major diameter of 0.375 inches (9.525 mm) and a pitch of 0.0417 inches (1.059 mm). The most common tolerance class is 2A for external threads and 2B for internal threads.
This page provides a complete engineering reference for 3/8-24 UNF thread dimensions and specifications, including thread designation, major diameter, pitch, threads per inch (TPI), minor diameter, and tolerance classes.
For engineers selecting threaded mounting solutions for electronic components such as feedthrough filters, EMI filters, RF shielding components, and precision assemblies, understanding the 3/8-24 UNF specification helps ensure proper mechanical compatibility, reliable installation, and long-term performance.
Quick Answer
The 3/8-24 UNF thread is a Unified National Fine (UNF) thread, which is primarily used in North America and widely adopted internationally in industrial and electronic applications.
3/8-24 UNF is a Unified National Fine thread specification where:
- 3/8indicates the nominal major diameter
- 24indicates 24 threads per inch (TPI)
- UNFindicates Unified National Fine thread series — characterized by finer pitch (more threads per inch) than UNC, offering greater strength and vibration resistance, though more susceptible to cross-threading
3/8-24 UNF Thread Tolerance Classes
Thread tolerance determines how tightly two mating components fit together.
The Unified Thread Standard defines several tolerance classes.
Class 2A / 2B Threads
Class 2 is the most commonly used commercial tolerance. Close to 90% of all commercial and industrial fasteners produced in North America use this class of thread fit.
External Thread: 3/8-24 UNF-2A
Internal Thread: 3/8-24 UNF-2B
Characteristics:
- Easiest assembly
- Best interchangeability
- Most industrial applications
Most commercial fasteners use Class 2.
Class 3A / 3B Threads
Class 3 provides a tighter fit.
External Thread: 3/8-24 UNF-3A
Internal Thread: 3/8-24 UNF-3B
Applications:
- Precision equipment
- Aerospace systems
- High-performance assemblies
Characteristics:
- Reduced clearance
- Higher positional accuracy
- Tighter manufacturing control
3/8-24 UNF vs Similar Thread Sizes
Engineers often need to determine whether another thread specification can replace 3/8-24 UNF.
3/8-24 UNF vs M10 × 1
| Parameter | 3/8-24 UNF | M10 × 1 |
| Standard | Unified | Metric ISO |
| Major Diameter | 9.525 mm | 10.0 mm |
| Pitch | 1.059 mm | 1.00 mm |
| Pitch Diameter | 8.837 mm | 9.350 mm |
| Minor Diameter | 8.265 mm | 8.917 mm |
| Thread Height | 0.574 mm | 0.541 mm |
| Thread Angle | 60° | 60° |
Frequently Asked Questions (FAQ)
Q1. What is the pitch of a 3/8-24 UNF thread?
24 TPI, equivalent to 1.058 mm pitch.
Q2. Is 3/8-24 UNF a metric thread?
No. 3/8-24 UNF is an inch-based Unified thread specification, not a metric thread.
Although its diameter is similar to some metric screws such as M10, the thread pitch is different.
Q3. What tolerance class is commonly used for 3/8-24 UNF?
The most common tolerance class is:
- External thread: 3/8-24 UNF-2A
- Internal thread: 3/8-24 UNF-2B
Class 3A/3B is used when tighter precision is required.
Q4. Is 3/8-24 UNF suitable for EMI filters?
Yes. It is commonly used in precision panel-mounted EMI and RF assemblies.
Engineering Support CTA: Selecting a threaded EMI filter or feedthrough capacitor? Share the thread standard and size, panel thickness, voltage/current, capacitance, and environmental requirements with LCA engineers. View Thread Mount Feedthrough Filters
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