Understanding Thread Types: UNC vs. UNF vs. Metric Threads

Understanding Thread Types: UNC vs. UNF vs. Metric Threads

A Guide to Choosing the Right Thread for Your Application

thread types play a critical role in how fasteners grip and hold materials. In this guide, we’ll explore the most common fastener thread types and when to use them.

1. What Are UNC thread types?

Purpose: UNC (Unified National Coarse) threads have fewer threads per inch (TPI), resulting in deeper, more widely spaced threads.

Why They Stand Out: Easier to assemble and disassemble, less likely to cross-thread, ideal for softer materials.

Characteristics:

  • Common TPI examples: 1/4″-20, 5/16″-18, 3/8″-16
  • Easier to assemble and disassemble
  • Less likely to cross-thread
  • Ideal for softer materials like aluminum, wood, or plastic
  • Better resistance to stripping in low-strength materials

Applications: Construction, Machinery assembly, Woodworking, Agricultural equipment

2. What Are UNF Threads?

Purpose: UNF (Unified National Fine) threads have a higher number of threads per inch, resulting in shallower, closely spaced threads.

Why They Stand Out: Provides better tensile strength, ideal for harder materials, more resistant to vibration loosening.

Characteristics:

  • Common TPI examples: 1/4″-28, 5/16″-24, 3/8″-24
  • Provides better tensile strength
  • Ideal for harder materials
  • More resistant to vibration loosening
  • Tighter tolerance fit

Applications: Automotive, Aerospace, Hydraulics, Precision instruments

3. What Are Metric Threads?

Purpose: Metric threads are standardized internationally and measured in millimeters (mm).

Why They Stand Out: Used globally across most industries, defined by diameter and pitch, internationally recognized standard.

Characteristics:

  • Defined by diameter and pitch (distance between threads), e.g., M6 x 1.0
  • Used globally across most industries
  • Pitch options: Coarse, Fine, Extra Fine
  • Thread angle: 60° (same as UNC/UNF)
  • Coarse metric threads are most common and equivalent to UNC

Applications: Automotive manufacturing, International machinery, Industrial equipment, Consumer products

Key Differences At a Glance

Feature UNC UNF Metric
Region USA USA International
Thread Pitch Coarse Fine Coarse/Fine (mm-based)
Common Materials Soft materials Hard materials All material types
Strength Moderate High tensile Varies by pitch
Ease of Use Easier to handle More precise Globally recognized

Choosing the Right Thread Type

When selecting a threaded fastener:

  • Use UNC for general-purpose fastening in soft materials and quick assembly.
  • Choose UNF when strength, vibration resistance, and precision are required.
  • Select Metric for international compatibility or OEM specifications.

Explore Thread Types on Our Site

Looking for specific thread types or need help selecting the right fastener? Visit our comprehensive selection of threaded fasteners: Shop Bolts & Threaded Fasteners

Need Help Selecting the Right Thread Type?

Our team at SC Fastening Systems can help you choose the perfect threaded fastener for your specific application.



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