Give me a hand… Right or Left?

Give me a hand… Right or Left?
“Lefty loosy, righty tighty.” If you have ever heard this saying to help you in remembering how to tighten a bolt, then you are familiar with the Handedness of a screw. The picture below helps with understanding the rotation and direction of threads. It’s called the “The right-handed rule of thread”, and it literally uses your right hand in determining the rotation and direction of a screw. If you decide to use this method beware, others may think your either really friendly and encouraging (flicking around a thumbs up), or flat crazy.
Right- and left-handed screw threads

Fingers are pointing in the direction of rotation for the direction of thrust (thumb direction)

The helix of a thread can twist in two possible directions. If you rotate the bolt you are using in the direction shown in the illustration above, you have what is known as a right-handed (RH) thread, because it follows the “Right hand grip rule”. It’s counterclockwise rotation removes the thread from the hole. Threads oriented in the opposite direction are known as left-handed (LH). If these were illustrated, then the left hand would be shown, and clockwise rotation on a left handed bolt would in fact loosen a left handed thread, removing it from the hole.

Because the world is made up of 60-90 % right handed people, right-handedness is the default handedness for screw threads, go figure (sorry left handed people). Therefore, most threaded parts and fasteners have right-handed threads. There are however very important applications for left handed threads. We’ve made a simple list:

  • When rotation of an object is in direct conflict with the loosening of the fastener, left handed bolts are generally used to tighten when rotated versus loosen. Examples include:
    • The left pedal on a bicycle.
    • Grinding wheels typically use left handed arbors
    • The securing nut on some circular saw blades – the large inertia at startup should tend to tighten the nut.
  • Turnbuckles and clamping studs work with right handed threads to contract and expand.
  • In some gas supply connections to prevent dangerous misconnections, for example in gas welding the flammable gas supply uses left-handed threads.

How does EZ Thread overcome this when repairing? We kid around with customers and joke about if they are fixing a left handed thread, then they have to use the tool in their left hands… We’re kidding. Like the left handed screw driver that never existed, EZ Thread doesn’t care what handedness you have on your thread. It works off of single flute repair tactics. Where other repair methods may have to have a specific size and pitch, EZ Thread just follows the thread path, and cleans away obstruction. Don’t waste time search for a left handed die, or the right pitch thread file… keep EZ Thread in the old tool box and be ready for anything. It’s that EZ!

Hopefully this article has helped those of us who still have to name out the months of the year to remember which one comes next. I know when the work week gets going and we all get a lot on our plates, it’s nice to have simple rules like this to help us through those brain hiccups. If you have never messed with threads, and genuinly didn’t know left handed threads existed, then hopefully we didn’t confuse you. Until next time, live, laugh, love, and be safe repairing those threads!


Posted on

November 4, 2015

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