TIL That screws are “righty tightly, lefty loosey” because right handed people are more common and arm supination(forearm rotation outward) is stronger than pronation(inward) for right handed individuals. This way tightening bolts uses the most torque. This is why you’re left hand can loosen easier.

Read more: https://en.wikipedia.org/wiki/Anatomical_terms_of_motion#Pronation_and_supination

What do you think?

12 Points
Upvote Downvote


Leave a Reply
  1. And also has a reason depending on direction of rotation of said fastener. If it applies counter clockwise force on fastener then you would just loosen the bolt rather than transfer power. A left handed thread would stay tigh and be able to transfer power. So it may be that as well

  2. I’m curious not being be a dick. With you saying

    “Supination is stronger than pronation for right handed people”

    Does that mean that pronation is stronger for left handed people or did you mean regardless of preferred hand?

Leave a Reply