Understanding Threading Terms

Welcome back to the third article in my special series, focusing on all things threading. In this article, we'll look at the essential “threading terms” that machinists should get to know.

Threads play a crucial role in the world of mechanical engineering, and to comprehend their intricacies, it's essential for machinists to familiarize themselves with the key threading terms.

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Let's explore some of these terms and their significance in various threading processes:?

1. Pitch (P): The distance from any point on a thread to the corresponding point on the adjacent thread, measured parallel to the axis.
2. Lead (Ph): The distance the thread advances for one revolution of the threaded assembly - I will cover this in another article.
3. Major Diameter (d): This is the largest diameter of the screw and is also known as the "nominal diameter" of the thread.
4. Minor Diameter (d1): The diameter of a thread at the minor cone or cylinder, also known as the "root diameter."
5. Pitch Diameter (d2): The diameter of a thread where the width of the groove equals the width of the thread.
6. Thread Depth (h): The distance between the crest and the root of a thread.
7. Crest: The top surface joining the two sides of a thread.
8. Root: The bottom of a surface joining the sides of two adjacent threads.
9. Flank: The inclined surface on either side of the thread ridge or crest.
10. Flank Angle (α): It is the angle between the inclined surfaces of the thread on either side of the crest.
11. Profile Angle (?): The angle formed by the two sides of the thread with each other. Therefore, for metric threads with a '60-degree flank angle', the profile angle would be '120 degrees'.
12. Thread length: This refers to the axial length of a threaded section that includes the full thread form at both the crest (top) and root (bottom) of the thread.

These terms are the foundation threading terms that all machinists need to know. Of course, there are many more terms like "lead angle, pitch line, dedendum, addendum" and many more, but for more threading terms, I would recommend checking out the Machining Doctor's website, where Erez Speiser shares his years of threading experience.?

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In the upcoming article, I’ll share the methods of “identifying and differentiating between left and right-hand threads” and shed some light on their applications. Until then, keep threading and stay tuned for more insights.