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The thread profile is more than just a simple shape—it’s a precise combination of dimensions and angles that determine how well a thread functions. While you don’t need to know all the details to cut a perfect thread, understanding some key elements can make a big difference, especially when choosing the right tap or die for your project. One such critical element is the **flank angle**.
The flank angle plays a vital role in defining the shape of the thread. It's the angle between the two flanks—the sloping sides of the thread—when viewed in cross-section. This angle is crucial because it affects how the thread engages with its mating part, influencing both **friction** and **self-locking properties**. For example, a smaller flank angle typically means a smoother, easier-to-turn thread, while a larger angle provides better holding power.
While many common thread types have standard flank angles, it's important to be aware of variations, especially when working with **foreign standards** or **motion threads**. A small mistake in the flank angle can lead to incompatibility, which is why it’s essential to verify what you're using before starting any project.
In the case of **pointed threads**, like the metric or imperial fastening threads, the most common flank angle is **60°**. However, British Standard Whitworth (BSW) and British Standard Fine (BSF) threads use a **55°** flank angle instead. This difference is significant, as mixing these can result in improper fit and function.
For **movement threads**, such as trapezoidal or saw threads, the flank angles are usually much smaller—around **30°** or **29°**, depending on the type. These are designed for applications where smooth motion is more important than tight sealing. The **ACME thread**, used in the US, has a slightly different angle of **29°**, making it distinct from its metric counterpart.
Some thread types, like certain **saw threads**, have **two different flank angles**—one for the load-bearing side and one for the non-load-bearing side. These asymmetrical designs are meant for specific applications where one direction of force is more important than the other.
Interestingly, there are also some older or less common thread types with unusual flank angles. For instance, the **steel armor pipe thread** has an unusually large angle of **80°**, and historically, there were even **0°** (right-angled) threads, which were eventually replaced due to their poor performance and difficulty in manufacturing.
No matter what kind of thread you're working with, having the correct **flank angle** is essential. At **BAER**, we offer a wide range of taps and dies tailored to meet the needs of every application. Whether you're dealing with standard fasteners or specialized motion threads, we’ve got the right tools to help you succeed. Explore our online store today and feel free to reach out if you have any questions—we’re always here to help.