How to recognize left hand vs right hand threads in lead screws
What is the difference between left-hand and right-hand threads and how can I recognize the thread direction?
A screw’s handedness indicates which direction the thread of the screw faces as it moves upward along the screw. In a right handed screw, the thread will move to the right as it slopes upward, and a left handed screw will move to the left as it slopes upward.
How to drive left-handed screws vs right-handed screws
The thread direction of a screw will determine which way it needs to be turned to be driven into a material. For right handed screws, turning them clockwise will drive them downward. For left handed screws, turning them counterclockwise drives them downward.
Thread direction in lead screws
Left-handed and right-handed screws are not just limited to standard fasteners — lead screws can also be manufactured in either thread direction. Thread direction plays a much more crucial role, however, in lead screw applications than in other types of screws.
Right-hand lead screw threads
For lead screws with right-hand thread, the thread flanks rise from bottom left to top right. In production drawings, right-hand threads are often marked with the letters RH. For example: TR20x4-RH.
Right-handed lead screws (and fasteners in general) are significantly more popular than their left-handed counterparts. However, this is often due to ergonomics, rather than technical differences. The majority of people are right-handed and can therefore apply more torque when turning a lead screw clockwise than counterclockwise, and the motion itself is more intuitive.
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Left-hand lead screw threads
A left-hand thread rises from bottom right to top left when viewed from the front. Production drawings will typically denote a left-handed thread with the letters LH. For example: TR20x4-LH.
Left-handed lead screws are popular in rotary applications where self-loosening is a concern. In these applications, the rotational movement can potentially cause a right-handed screw to loosen over time. By instead using a left-handed screw, this same motion will instead keep the screw tightened and secure.
Other applications like turnbuckles or actuators that need to move two screws together and apart in sync also rely on left-handed screws, or a double-ended (reverse) screw with a left-handed thread on one side and a right-handed thread on the other that meet in the middle of the screw.
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What other thread directions does igus® offer?
Thread directions other than left and right, are of course, impossible. But what about a combination of both cutting directions?
The dryspin product range of lead screws include left-handed, right-handed, and reverse lead screws in each of the major lead screw thread profiles, as well as a proprietary high-helix thread perfect for achieving a long service life and smooth, efficient motion.
If you'd like advice on how to determine the best lead screw for your application, contact us. You can also visit this webpage to learn more about dryspin® lead screw assemblies or to try out our lead screw product finder and lead screw configurator to calculate service life, build lead screws in 20 minutes or less, and more.
Frequently Asked Questions
The difference lies in the direction of the helix (the spiral of the thread) and the resulting motion. A right-hand (RH) thread tightens/advances when rotated clockwise (following the "righty-tighty" rule). A left-hand (LH) thread tightens/advances when rotated counter-clockwise.
Right-hand (RH) thread is the standard and most common choice across all industries for both fasteners and lead screws. LH threads are considered specialized.
The primary reason is to prevent self-loosening. In machinery with a consistent rotational force that would naturally unscrew an RH thread (like a circular saw blade nut or a left bicycle pedal), an LH thread is used so the operating rotation actually causes it to tighten.
No. The direction of the thread (handedness) does not affect the performance characteristics like load capacity, efficiency, or lead (travel distance per revolution). These factors are determined by the thread profile (e.g., ACME, trapezoidal, high helix) and pitch/lead.
Absolutely not. The threads are incompatible. Attempting to match a left-hand nut with a right-hand screw (or vice versa) will cause the threads to cross, preventing proper engagement and tightening.
In applications like turnbuckles or linear actuators that need two separate carriages to move simultaneously, a single shaft is machined with RH threads on one end and LH threads on the other. Rotating the shaft moves the two nuts either closer together or farther apart.
Yes. In the gas industry, fittings for flammable gases (like propane or acetylene) are often given left-hand threads to prevent them from being accidentally connected to regulators designed for non-flammable gases (like oxygen), which use standard RH threads.
When you look at the threads on the screw: if they slope up and to the right, it's a right-hand thread. If they slope up and to the left, it's a left-hand thread.
