I’m curious if the black axles and the silver stainless steel ones are the exact same metal, just with a different finish. :-\ If so, what is the finish on the black one called? Is there any benefit to the black finish?
Thanks.
I’m pretty sure it’s black zinc and nickel plated.
Black zinc has more corrosion resistance. 
Okay, thank you. 
The HSPIN black axle was supposed to be a stronger steel alloy than generic silver colored screws. In my experience the strength of screws and bolts varies across the spectrum, though I’m sure there is some hardness standard that manufacturers use for the different grades. Generally genuine stainless are the hardest, followed by black with generic common zinc plated screws the least strong. There are harder alloys using carbide and other metals but they tend to be too brittle in most cases.
Interesting, do they use stainless? I thought they were just plated.
Good question on the alloys used. I wonder if there really is that much difference between most screws.
I kind of doubt that specialty screws are manufactured for yoyos rather than various off the shelf options out there. Also how durable would they need to be in the first place?
This just opened up a can of worms in my head!
I just put the one in the right in one of my yo-yos, and it literally smoothed right out. I don’t know what kind of metal it is, I think just alloy steel, not sure. But, all these axles don’t seem to be created equal. The one on the right is shaped a little bit different (check the ends and threads). Maybe the shape was enough to tune the yo-yo. I didn’t even care about smoothness, but it was purely coincidental.
https://farm4.staticflickr.com/3744/19661483792_ed7b9dc899_z.jpgAxle1 by Total Artist, on Flickr
I believe the finish on the black axle above is called Black Oxide.
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Thanks. The guy in the hardware store did mention there was something on it to prevent oxidation, he just never said what it was specifically. That got me thinking about it.
The threads on the black oxide screw look to be fuller and better formed. Probably fit the threads in the shell better. Some screws fit better in a female thread.
I don’t think it’s black oxide as if it were, it would likely be coated in a grease to prevent corrosion as black oxides are generally SUPER thin and provide little protection of the metal below.
And I might be wrong about the zinc coating. Could be a phosphate coating which is more common.
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I agree, it’s probably cut for a more precise fit into those threads of the yo-yo half. It really surprises me the difference it made in how the yo-yo plays.
I’ve never bought any hardward labeled “black oxide” that had any grease on it.
If it’s used outdoors, black oxide is going to rust unless it has some kind of coating on it, grease, oil, whatever.
But since it’s a yoyo, I guess a black oxide would be fine since it shouldn’t ever get wet or have to worry about salt.
That said, is stainless not always used cause the alternatives might be cheaper without really affecting anything?