As does the left-hand pedal on a bicycle.
Agreed, but note that this is about right-handed vs. left-handed threads, which is different. If you point your thumb in the direction of the bolt tip, then turning it according to the way your (right hand) fingers curl will always mean tightening.
Likewise, if imagine gripping Earth with your hand, with your thumb pointing north, then it turns in the direction that your fingers curl.
And if I use my left hand? It depends on the frame of reference.
Your left hand gives the wrong answer. Again, you have to decide the preferred direction–in the case of the screw, it’s towards the tip–but it doesn’t depend on your frame of reference.
I had the exact same question when I was a kid. My dad was watering the lawn and sent me to turn off the water faucet. I asked him “which way is off?”, and he said “to the right.” I looked at the knob on the faucet and saw that if the top was going to the right, then the bottom would be going to the left. I couldn’t exactly put that into words at that age, and didn’t want to raise my dad’s ire. I eventually figured out that “to the right” or “to the left” refers to the top of the item being turned.
I’d forgotten about those.
I used to drive an MG with wire wheels, and a single, large nut to hold each wheel on.
The threads were different on the right and left sides of the car, but I don’t recall which was right-hand thread and which was left. Each nut was labeled with “UNDO” and an arrow.
I’ve seen plenty of cop shows where the ballistics expert says “five lands and grooves with a right twist” to describe the markings on a bullet. Since they specify which twist, I assume some guns have right-hand rifling, and some are left.
Yeah, there isn’t a preferred direction of bolt threads. Curl your fingers one way, and the bolt (nut, screw, etc.) moved in the direction of your thumb. Curl the other way, and it still goes in the direction of your thumb. It’s kind of arbitrary that right-hand threads predominate, but once you remember that, everything else follows consistently.
Is it arbitrary that right-hand threads are more common? I wouldn’t be too surprised if it traced back to right-handed blacksmiths, or something like that.
Maybe we’re talking at cross-purposes, but it seems to me that as soon as you say “you have to decide the preferred direction - in the case of the screw, it’s toward the tip”, you are defining a frame of reference.
I understand how, say, a steering wheel could be confusing, since the bottom moves left while the top moves right. And that’s reversed if you imagine the wheel from the other side. But if you decide that your thumb points along the connection with the car, then there’s no confusion: use your right hand to turn right, and left hand to turn left. This works no matter which way you’re turned–upside down, backwards, whatever.
A screw is the same way. If you’re ever working to tighten something blindly, maybe on the other side of some panel, and you can’t quite work out which way to turn it–just point your right-hand thumb toward the thing you’re trying to screw in, and see which way your fingers curl. It works in all orientations.
Consensus seems to be that it has to do with 90% of people being right-handed. Gunsmiths made most of the few metal screws in use before machine made screws were produced. Up until then large wooden screws were most common. It’s supposed to be easier for right handed people to turn the hand and wrist clock-wise most easily.
And this reminds me that clockwise is considered the ‘pronate’ motion for the right hand. So winches and along with threaded devices will prefer a clockwise direction for the vast majority of humans.
I don’t hear these terms much anymore, but curlers talk of “in turn” and “out turn” shots. I’m right-handed, so the stone will be out in front of me in my right hand. If I bring my elbow and wrist in toward my body as I release the stone, that will give it a clockwise rotation (when viewed from above) and it will curl to the right. That’s an “in turn”. “Out turn” is the reverse; the wrist and elbow move away from my body, the stone rotates counter-clockwise and curls to the left.
Directions are reversed for lefties; the “out turn” rotates clockwise and curls to the right.
Strangely, curling stones behave differently from most other things. If you slide a glass along a table or bar, and give it a clockwise rotation, it will curve to the left.
Why would they be different? Is it an anti-torque motion with the glass, but the stone is too heavy and there’s too much momentum in the stone to overcome that?
There have been academic papers published on that very topic. I believe the currently accepted theory is that the front edge of the stone creates tiny, angled scratches as the stone slides, and the trialing edge gets slightly deflected by those scratches.
There’s a video here that explores a few different theories. For extra coolness points, that was filmed at my club.