It’s all standard sizing, like most metal yo-yos these days… nothing special about it. Oh wait you meant length? Yeah I guess that can vary depending on how deep the axle is tapped into each side 
But I don’t think it would vary all that much from yo-yos of similar size and shape, so that’s my suggestion. Don’t compare it to, say, a CLYW with a giant axle protrusion on each side of the cup, of course!
It is a good idea to replace the axle if you are troubleshooting significant vibe.
One yo-yo I dropped off an Iowa State fair ride had terrible vibe (my fault, lol) and replacing the axle reduced that vibe by 50% easily. Still vibe-y but wayyy better.
I read on reddit that it’s a 10mm long M4 axle.
Source: https://www.reddit.com/r/Throwers/comments/3bjndl/myy_n12_axle_size_update/
That was my source too…