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Understanding Thread Types

Understanding Thread Types

Once you’ve got the basics of the different types of fasteners down, the sheer amount of different types of threads can be a bit overwhelming. Each type has its own unique applications, advantage and characteristics. This article will highlight the most common types. As always, you can email our sales reps at sales@knappfast.com if you need help with anything.

Threaded fasteners, such as nuts and screws, are used in almost all applications that require a type of fastener. They’re used across all industries from electronic boards to aerospace. They work by mating a male threaded component (such as a bolt) with a female threaded component (such as a nut) to create a secure joint which is often adjustable.

Important characteristics of thread:

  • Pitch: The distance between threads, usually measured in millimeters or threads per inch (aka TPI).
  • Diameter: The nominal diameter of the fastener, important for ensuring compatibility with the corresponding hole or nut.
  • Thread Angle: The angle formed between the flanks of the thread, which can affect the strength and holding power of the fastener.

The most popular types of thread are listed below.

Unified Thread Standard (UTS)

UTS is one of the most widely used thread systems, particularly in North America. It is often listed in this format: 3/8”-16. Where “3/8” indicates the diameter and “16” is the pitch.

  • UNC (Unified National Coarse): Coarse threads are more resistant to stripping and are faster to assemble, making them ideal for general purpose applications where quick assembly is needed.
  • UNF (Unified National Fine): Fine threads offer greater tensile strength and better adjustment capabilities, making them suitable for precision applications.
  • UNEF (Unified National Extra Fine): Used for specialized applications where fine adjustments are critical.

Metric Threads

Metric threads are standardized globally and measured in millimeters. They are characterized by their thread pitch and diameter, such as M10 x 1.5, where “M10” indicates a 10mm diameter and “1.5” is the pitch.

  • Coarse Threads: Commonly used due to their balance of strength and ease of assembly.
  • Fine Threads: Provide better clamping force and are used in applications requiring higher precision.

Acme Threads

Acme threads are a trapezoidal shape and are used in applications where large loads are expected, such as in lead screws and industrial machinery. They provide a strong thread profile with a larger contact area, enhancing load distribution.

Pipe Threads

Pipe threads are designed for sealing pipes and fittings. They can be tapered to varying degrees or straight and are crucial for ensuring leak-proof connections in plumbing and fluid systems.

  • National Pipe Thread (NPT): Commonly used in North America, these threads are tapered to create a tight seal.
  • British Standard Pipe (BSP): Includes BSPT (tapered) and BSPP (parallel), used widely in the UK and internationally for plumbing and gas fittings.

British Threads

British threads, aside from the pipe ones listed above, are integral to various engineering and construction applications, particularly in the UK and many former British colonies. British Standard Whitworth (BSW), is one of the oldest thread types, BSW threads have a rounded root.

Overall, understanding the various thread types and being able to identify them, is essential for selecting the right fasteners for your project. Each thread type offers unique advantages and is suited for specific applications. By familiarizing yourself with these differences, you can ensure the reliability, safety, and efficiency of your assemblies. Whether you’re working on a simple DIY project or a complex industrial application, the right choice of threaded fasteners can make all the difference. Please contact our sales department with any questions you may have at sales@knappfast.com.

Check out our comparison chart resource document as well which references standard coarse and fine thread imperial and metric diameters.