Threads are a common feature shared by all screws. Whether it’s a wood screw, machine screw, drywall screw, sheet metal screw or any other type of screw, it will feature helical ridges. Known as threads, these ridges act like teeth. They grip the material in which they are driven to create a strong and secure hold.
Not all screw threads are the same, however. Some of them are coarse with fewer threads per inch (TPI), whereas others are fine with more TPI. There are also left-hand and right-hand screw threads. By familiarizing yourself with the differences between left-hand and right-hand threads, you can choose the right type for your next project.
What Are Right-Hand Threads?
Threads are classified as right-hand or left-hand depending on their orientation. In other words, the direction of a screw’s helical ridges will determine whether it has right-hand or left-hand threads.
Right-hand threads slope up and to the right. Right-hand threads typically begin either below the screw head or about halfway down the shank. From here, they slope up and to the right. You can tighten screws with right-hand threads by turning them clockwise.
What Are Left-Hand Threads?
Left-hand threads slope up and to the left. Like with right-hand threads, they typically begin either below the screw head or halfway down the shank. Rather than sloping up and to the right, though, left-hand threads slope up and to the left. You can tighten screws with left-hand threads by turning them counterclockwise.
Differences Between Right-Hand and Left-Hand Threads
Right-hand threads are more common than left-hand threads. About nine in 10 threaded fasteners feature right-hand threads. In fact, unless a fastener explicitly mentions left-hand threads, it probably has right-hand threads. It’s the standard for most screws and bolts.
Left-hand threads are less common. They are typically used in specific applications, such as the pedals on a bicycle or rotating machinery.
Right-hand and left-hand threads are installed, as well as removed, in different directions. As previously mentioned, fasteners with right-hand threads are tightened via a clockwise direction, while fasteners with left-hand threads are tightened via a counterclockwise direction.
You’ll need to turn the fasteners in the opposite direction to loosen and remove them. For right-hand threads, turning the screw counterclockwise will loosen and remove it. For left-hand threads, turning the screw clockwise will loosen and remove it.
In Conclusion
You can distinguish between right-hand and left-hand threads by their direction. If the threads rise from left to right, the fastener has right-hand threads. If the threads rise from the right to left, the fastener has left-hand threads.