Comparison of Metric and Unified National Coarse Threads

Metric and UNC are two major standards with different measurement systems.

Metric is the global standard; UNC is standard in North America.

Choose Metric for new designs; use UNC for North American retrofit.

Overview

Metric threads use millimeter measurements and are the global standard.

UNC uses imperial fractions and TPI measurement; dominant in North America.

They are not interchangeable but perform similarly.

Size Comparison

When to Choose Metric

• New product design
• International/global markets
• Modern industries (automotive, electronics)
• Future-proof applications
• Easier calculations (decimal-based)
• Better global supply chain

When to Choose UNC

• Retrofitting North American equipment
• Domestic US/Canada only
• Legacy systems
• HVAC and plumbing standards
• Lower North American costs
• Established tooling and expertise

Technical Comparison

Conversion

Approximate conversions (not exact):

• 1/4″-20 UNC ≈ M6×1.0
• 3/8″-16 UNC ≈ M10×1.5
• 1/2″-13 UNC ≈ M12×1.75

Always verify actual requirements before converting.

Best Practice

• New designs: choose Metric
• Retrofits: keep existing standard
• Global operations: Metric mandatory
• Never mix both in same assembly

Related Engineering Resources

Thread Standards

• Unified Thread Standard
• Metric Threads
• BSP Threads
• NPT Threads

Thread Dimensions

• Thread Pitch
• External Thread
• Internal Thread

Thread Guide

• Thread in EMI Filters
• Measure Pitch
• Measure TPI
• How to Identify an Unknown Thread

Related LCA Products

• Thread Mount Feedthrough Filters

Related LCA Products

Threaded EMI & Feedthrough Components

Thread dimensions are an important part of mechanical compatibility when selecting threaded electronic components.

LCA provides threaded EMI/EMC and feedthrough components with various thread configurations for electronic, RF, instrumentation, aerospace, and other applications.

Typical configurations may include:

• Thread Mount Feedthrough Filters
• Threaded Feedthrough Capacitors
• Hermetically Sealed Feedthrough Filters
• Miniature RF Filters
• Custom Threaded EMI Components

If the required thread is not available as a standard configuration, LCA can evaluate custom thread sizes, mounting dimensions, housing configurations, and other mechanical requirements.

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