5/16-18 UNC Thread Dimensions & Specifications

5/16-18 UNC Thread Quick Specifications

Introduction

As a representative specification within the Unified Thread Standard (UTS) framework, the 5/16-18 UNC thread is extensively utilized across North America and finds broad application in global industrial manufacturing and electronic engineering sectors. This thread specification adheres to the inch-based dimensional system and is designated through a standardized nomenclature.

This page presents a systematic engineering reference for the 5/16-18 UNC thread, encompassing its thread designation, major diameter, pitch, threads per inch (TPI), minor diameter, and tolerance classes.

For engineers and technical professionals engaged in the design and selection of threaded mounting solutions for components such as feedthrough filters, EMI filters, RF shielding components, and precision assemblies, a comprehensive understanding of the 5/16-18 UNC thread’s geometric characteristics and tolerance framework is of significant engineering value to ensure mechanical compatibility, achieve assembly reliability, and guarantee long-term system performance.

Quick Answer: The 5/16-18 UNC thread belongs to the Unified Thread Standard (UTS), which is primarily used in North America and widely adopted internationally in industrial and electronic applications.

5/16-18 UNC is a Unified National Coarse thread specification where:

• 5/16indicates the nominal screw size number (5/16 screw size)
• 18indicates 18 threads per inch (TPI)
• UNCindicates Unified National Coarse thread series

Per the Unified Thread Standard (UTS), the 5/16-18 UNC features a nominal major diameter of 0.312 inches (7.925 mm) with the standard 60-degree unified thread form.

Balancing moderate footprint and robust mechanical load-bearing capability, this thread grade is widely adopted for hardware mounting scenarios with constrained installation envelopes. It sees heavy deployment across high-reliability electronic and mechanical domains.

Common applications include:

• Electronic enclosures
• Precision mechanical assemblies
• PCB-mounted fastening hardware
• RF&microwave hardware assemblies
• EMI-shielded structural sub-assemblies
• Test and measurement instrumentation
• Avionics and aerospace-grade electronics

5/16-18 UNC 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.

External Thread: 5/16-18 UNC-2A

Internal Thread: 5/16-18 UNC-2B

Characteristics:

• Balanced fit
• Good manufacturability
• Low mass-production costs
• Suitable for general industrial applications

Most commercial fasteners use Class 2.

Class 3A / 3B Threads

Class 3 provides a tighter fit.

External Thread: 5/16-18 UNC-3A

Internal Thread: 5/16-18 UNC-3B

Applications:

• Precision equipment
• Aerospace systems
• High-reliability and high-performance mechanical assemblies

Characteristics:

• Reduced clearance
• Higher accuracy
• Higher manufacturing requirements
• Strict manufacturing and inspection standards

5/16-18 UNC vs Similar Thread Sizes

Engineers often need to determine whether another thread specification can replace 5/16-18 UNC.

5/16-18 UNC vs M8 × 1.25

This is one of the most common comparisons.

Frequently Asked Questions (FAQ)

Q1. What does 5/16-18 UNC mean?

5/16-18 UNC is a Unified National Coarse thread designation. The number “5/16” represents the screw size number, “18” indicates 18 threads per inch (TPI), and “UNC” means Unified National Coarse thread series.

A 5/16-18 UNC thread has a nominal major diameter of approximately 0.312 inches (7.925 mm) and uses a 60-degree Unified thread profile.

Q2. Is 5/16-18 UNC a metric thread?

No. 5/16-18 UNC is an inch-based Unified thread specification, not a metric thread.

Although its diameter is similar to some metric screws such as M8, the thread pitch is different.

Q3. What tolerance class is commonly used for 5/16-18 UNC?

The most common tolerance class is:

• External thread: 5/16-18 UNC-2A
• Internal thread: 5/16-18 UNC-2B

Class 3A/3B is used when tighter precision is required.

Q4. Can LCA provide EMI filters with 5/16-18 UNC threads?

Yes. LCA supports customized EMI feedthrough filter designs with various thread configurations, including miniature inch and metric thread options.

Customization may include:

• Thread size
• Housing dimensions
• Electrical parameters
• Sealing structure
• Plating options

Q5. What application scenarios are 5/16-18 UNC threaded EMI filters suitable for?

Featuring reliable mechanical strength and universal mounting compatibility, 5/16-18 UNC threaded EMI filters are commonly used for aerospace electronics, precision mechanical assemblies, industrial instrumentation, and RF/microwave shielding systems, ensuring stable EMI suppression and long-term assembly reliability in high-reliability electronic equipment.

Engineering Support CTA: Selecting a threaded EMI filter or feedthrough capacitor? Share the thread standard and size, panel thickness, voltage/current ratings, target capacitance value, and environmental operating requirements with LCA engineers to obtain professional tailored technical support and product solutions. View Thread Mount Feedthrough Filters

Related Engineering Resources

Thread Standards

• Unified Thread Standard
• UNC Threads
• UNF Threads
• UNEF Threads
• Metric Threads

Thread Specifications

• #8-32 UNC Thread Dimensions
• 3/8-16 UNC Thread Dimensions
• 1/4-28 UNF Thread Dimensions
• #12-32 UNEF Thread Dimensions

Thread Guide

• Thread in EMI Filters
• Thread in Feedthrough Capacitors

Related LCA Products

• Thread Mount Feedthrough Filters