I noticed that virtually no recent yo-yos have either an axle nut (metal), or an axle hole. But lots of older yo-yos do.
Also see the 2008 OneDrop M1 and 2007 OneDrop Project…
Or compare old Genesis and new Genesis!
Why did axle nuts and axle holes fall out of favor?
Did machining get better in the last 10 years, or was it an aesthetic thing, or … ? I have to agree that “belly buttons” don’t look great on yo-yos, though.
Playaz wanna fingerspin, brah.
Maybe! But it looks like this was on its way out before fingerspins became a big thing? I don’t know what year that was. You can see the flat side of the “modern” genesis, above, isn’t exactly a fingerspin-friendly dimple.
I imagine it has to do with reduction of weight and increasing of precision and balance? The bolt head, and nut are adding extra mass that may not be needed or wanted? im not sure, just spit balling.
Also it could be an asthetic that some of the consumers/makers want to see/make a more refined, less industrial feel?
/shrug
The nut requires the yoyo to be worked on a mill. Every modern yoyo I can think of is entirely machined on a lathe. This leads to a much more smooth throw, as well as reduced manufacturing costs
Edit- notice on the post with the center nut yoyo, there is engraving on the edge of the rim. That’s also a dead giveaway of millwork
I think we’re all yoyo nuts but we’re not axle holes! 
How so? Please explain. Any yoyo can be engraved.
The mill work (includes hub and rim machining) could all be done in one step, more or less, depending on the machine or machines. You’re correct in saying that any yoyo can be engraved but setting up/ indicating a part on multiple machines adds dramatically to the labor costs. It’s totally possible to mill whatever you want on the rim of any yo-yo, but for yo-yos with a milled hub it’s more feasible since the yoyo is in the machine already
Edit- maybe “dead giveaway” wasn’t the best word choice but it’s a good indicator on older yoyos
2 of my favorite finger spin yoyos both have axel holes 
Curvy donut man and Elysian 
Wish I had an Elysian… For some reason fingerspin yoyos honestly haven’t gotten any better since its release.
Sure some yoyos might be able to fingerspin longer but catchability and ease of hops aren’t super amazing with the vast majority of centering fingerspin yoyos. I wish it wasn’t the case but it’s why I still prefer a good flat cup yoyo for more advanced fingerspin tricks
I just realized a full hole all the way through the yo-yo means you have to be careful threading the axle since it could be too far to the “left” or “right” of the yo-yo and thus be not centered.
One Drop had this to say:
It’s actually easier and more consistent to make it with the hole. Tapping works much better when you can evacuate the chips on the other side. A “blind” tap is more difficult from machining terms.
But as mentioned, players don’t really like that “belly button” style.
I was thinking that steel on steel threads (with the metal nut) has to be a bit safer for long term longevity, but One Drop went and solved that so cleverly with their side effects system. But alu threads must be OK long term because there are still plenty of OD models – and virtually every other yoyo maker – use standard Alu tapped threads.
Also thanks for the reminder @Cannon I forgot Curvy Donut Man is one of the rare recent / new yoyos with the hole! I even have this one and I forgot about the hole!
Sturm Panzer Pakfa and One Drop Format:C have the axle hole too.
I was thinking, if the goal is absolute minimal center weight then you definitely want the blind tapped aluminum threads… and technically you want to make the hole go all the way through, though I can’t imagine that tiny amount of aluminum would amount to more than the smallest fraction of a gram!
But if your goal is to reduce center weight to an absolute minimum…
There’s no way a metal nut is going to be lighter than having bare threads in aluminum.
A very short steel axle (or if you’re feeling super fancy, a titanium axle ala the Edge Beyond) will reduce center weight even further.
Both alu threads and a short axle are more risky, but that risk seems to be minimal given the thousands of yo-yos out there with aluminum tapped thread holes and short steel axles that are doing just fine. Yeah, there’s some stripping that happens (and it is a major bummer when it does, because it is super hard to recover from) but it’s not like an epidemic of aluminum threads getting stripped out of yo-yos today?
I’m not totally sure how important minimal center weight is to the design of a yo-yo? My gut feeling is that the ratio of rim weight to everything else is more important? That said, I did once have these weird cheap off-brand chinese yo-yos I got off Amazon (as an experiment) that had a big metal nut for the axle along with hubstacks (even more center weight!) and that definitely wasn’t a good feel.
I also remember people being paranoid that over tightening a yo-yo with a drill-thru axle hole (I think the Burnside had this design) would send the axle through the cup wall. Not the milled design with the nut, just the regular axle but the cup was drilled thru with a hole slightly smaller than the axle itself, like what a countersink bit would do.
Ah right, so there is a “backstop” preventing you from screwing it all the way through the cup. Makes sense.
Your intuition is correct - axle hubs/matador spikes are already very efficient. I checked this in CAD and lopping off the hub so that the axle goes all the way through only saves 0.15-0.20g depending on the shape of the hub. You actually save more weight (0.25g) by switching from a stainless steel axle to a titanium axle, which also doesn’t require changing the design of the cup.
Is the Elysian a good yoyo? never heard of it before.
It’s an amazing yoyo! If you can get your hands on one, I would highly recommend it! They don’t come up for sale too often though.
Okay, better look into it then.
