Left-Handed and Right-Handed Fastener Threads: Uses and Comparison


Fasteners are the nuts, bolts, screws, and other small components that keep machinery and components together in working order. Many fasteners work through the effective use of threads (left-hand thread and right-hand thread), which allow nuts and bolts to screw together effectively.

Screw Thread

But how do threads work? The direction in which workers screw and unscrew fasteners has a lot to do with the applications in which they appear. Additionally, many different types of threads exist to optimize different ways to fasten objects. In this blog, we explore a few of the many different varieties of threads as well as their uses.

Common Uses and Applications of Fastener Threads

Screw threads help with many different applications, such as:

  • Fastening: Screw threads appear on traditional fasteners such as nuts, bolts, and screws, and they also help connect threaded pipes, hoses, caps, and fixtures
  • Gear reduction: Screw threads help with gear reduction by using worm drives
  • Linear object movement: Fastener threads can be used to convert rotary motion to linear motion


Understanding Right-Handed vs. Left-Handed Threads

Thread Terminology and Different Types

Threads are continuous helical ridges on cylindrical fasteners. For parts such as screws, the ridges will be on the exterior, and parts like nuts have ridges inside of their cylindrical bodies.

There are a number of common terms to describe different aspects of threads, which we define below:

  • External threads: Threads that wind around the exterior of a fastener’s shaft
  • Internal thread: Threads that run along the inside of a fastener
  • Axis: Longitudinal lines used to measure the length of the fastener
  • Pitch: The distance between a point on one thread to a point on another thread
  • Major diameter: The largest internal or external thread diameter
  • Minor diameter: The smallest internal or external thread diameter


Fastener Threads: What is a Screw Thread?

Screw threads are sloped helices that spiral down the cylindrical surface of parts like screws and bolts. They’re responsible for converting energy between rotational and linear movement and force. Fasteners with compatible threads can provide tight seals for a wide variety of equipment.

Screw Handedness: Left-Hand Thread and Right-Hand Thread

Screw handedness refers to the direction that a screw’s thread wraps around its shaft. Right-handed threads run clockwise, and left-handed threads run counterclockwise. The origin of a thread’s handedness is rooted in human physiology: Screws with different handedness are ergonomic for people depending on their dominant hands.

Most screws today use right-handed threads, and it’s rare to find a left-handed screw used in any application that doesn’t specifically call for it. However, there are some applications that specifically call for the use of left-handed fasteners.

Uses and Applications of Left-Handed Threads

Left-handed threads are also known as reverse threads. These threads are used in specialized applications in which the application of pressure would force a right-handed screw or bolt to come loose.

left hand thread screw

Some applications that benefit from the use of left-handed fasteners include:

  • Automotive: Some tires’ bolts are reverse threaded to keep torque from loosening them
  • Heating and plumbing: Pipes are often fitted with both right- and left-handed threads to provide an extra layer of defense from leakage
  • Safety: Gas-supply valves use left-handed threads to differentiate them from the valves that control oxygen

Quality Fastening Solutions by National Bolt

National Bolt builds custom nonstandard fasteners, large-diameter products, and more, and we pride ourselves on our quick turnaround and delivery times.

custom nuts bolts and washers

If you would like to learn more about our custom fastening solutions, don’t hesitate to reach out to us or request a quote today!


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