Publication : December 10, 2024

Understanding the Difference Between UNC and UNF Threads

In the industrial world, choosing the right type of bolt is essential to ensure the strength and safety of assemblies. Among the standards, UNC (Unified National Coarse) and UNF (Unified National Fine) threads are the most commonly used. This guide aims to clarify their differences and specific applications to help you make the best choice.

First of all, it is important to know that the number related to the type of bolt is equivalent to the number of turns possible on 1 inch of length. For example, if we look on a #10-24 bolt, the number 24 indicates the number of threads per inch (TPI).

Now here are the differences between UNC and UNF threads:

What is UNC thread?

UNC, or Unified National Coarse, threads are characterized by more widely spaced thread pitches. This means that the threads are larger and fewer in number per unit length.

Benefits of UNC Thread :

Better Shear Strength : Ideal for softer materials, such as aluminum or wood, where a fine thread might strip.
Fast Installation : Due to the wider spacing, UNC bolts are easier to drive, even in dusty or dirty environments.
Reduced Risk of Galling : Due to the wider threads, galling is less common.

Common Applications:
UNC bolts are often used in environments where strength is a priority, such as:

Steel construction assemblies.
Fastenings in timber structures.
General applications where vibration is not a major problem.

What is UNF Thread?

UNF, or Unified National Fine, threads have closer thread pitches, with finer and more threads per unit length.

UNF Thread Advantages:

Stronger Fasteners : Stress distribution is better, reducing the risk of loosening.
Aesthetics and Precision : Perfect for applications where precise fit is crucial.
Better Performance in Hard Materials : UNF bolts penetrate hard metals such as steel more easily.

Common Applications:
UNF bolts are preferred in industries requiring high precision and vibration resistance:

Automotive (e.g. engines, suspensions).
Aerospace.
Mechanical assemblies subject to constant vibration.

How to choose between UNC and UNF?

1. Material type:

Prefer UNC for soft materials such as aluminum or wood.
Opt for UNF if you are working with steel or other hard metals.

2. Operating environment:

In the presence of dirt or dust, UNC bolts will be more suitable thanks to their wide profile.
If vibrations or mechanical stresses are significant, UNF offers better holding power.

3. Required strength:

UNC is suitable for robust but non-critical fasteners.
UNF is ideal for assemblies requiring high clamping force.

Criteria	UNC thread (Unified National Coarse)	UNF thread (Unified National Fine)
Thread spacing	More spaced, bigger nets.	Closer together, finer threads.
Suitable materials	Soft materials (wood, aluminum).	Hard materials (steel, tough metals).
Shear strength	Superior thanks to wider threads.	Slightly lower than UNC.
Precision and aesthetics	Less precise, more for general assemblies.	More precise, suitable for technical applications.
Vibration resistance	Less efficient against vibrations.	Better hold in vibrant environments.
Performance in dirty environments	Ideal: Wide nets are more resistant to dirt.	Less suitable for dusty conditions.
Ease of installation	Faster and less risk of seizure.	Requires more precision during installation.
Main applications	Construction, general assemblies.	Automotive, aeronautics, mechanical equipment.

Adapt the choice to your industrial needs

Understanding the differences between UNC and UNF is crucial to maximize the efficiency and longevity of your assemblies. At AB Industriel, we offer a wide range of bolts that meet both standards. Our team is at your service to help you identify the solutions best suited to your industrial projects.

Need additional advice?

Do not hesitate to consult our product catalog or contact us directly. Together, let's optimize your assemblies for optimal performance.

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