A screw’s thread pitch plays an important role in its holding power. Screws with a fine thread pitch typically have greater holding power than those with a coarser thread pitch. What is thread pitch exactly, and how does it affect a screw’s holding power?
What Is Thread Pitch?
Thread pitch is the distance between the threads on a screw. All screws have threads. Consisting of helical ridges, they allow screws to be driven into objects. As you press and turn a screw against an object, the threads will dig into the object while simultaneously scooping out material. The distance between a screw’s individual threads, however, varies depending on the thread pitch.
Metric vs U.S. Thread Pitch
In metric screws, thread pitch is measured in millimeters. It’s not uncommon for metric screws to have a thread pitch of 1.5 to 1.25 millimeters, meaning the distance between the individual threads are 1.5 to 1.25 millimeters.
In U.S. screws, thread pitch is measured in threads per inch (TPI). As the name suggests, TPI represents the total number of threads per inch. Some U.S. screws have a TPI of 20, whereas others have a TPI or 25 or higher.
Gripping Objects
Thread pitch will affect a screw’s ability to grip objects. A fine thread pitch will result in more points of contact. As a result, the screw will create more friction and have a better grip on the object. A coarse thread pitch, on the other hand, will result in fewer points of contact but deeper grooves. This can make coarse screws a good choice for soft materials, such as wood.
Resistance to Loosening
Screws with a fine thread pitch are better protected from loosening. They are able to distribute the force across more points of contact. Therefore, screws with a fine thread pitch are harder to pull out and more resistant to loosening than those with a coarse thread pitch.
Shear Strength
A fine thread pitch translates into greater shear strength. Screws with a fine thread pitch have a larger minor diameter than those with a coarse thread pitch. This design translates into greater shear strength, which improves the screws’ holding power.
In Conclusion
Always check the thread pitch when shopping for screws. It represents the distance between a screw’s threads. Some screws have a fine thread pitch, whereas others have a coarse thread pitch. Regardless, it will influence their ability to grip objects, resistance to loosening and shear strength.
