These axles come in 8mm, 10mm, and 12mm sizes.
Sochi wanted to be able to provide axles, because not a lot of equipment brands do that. We're all guilty of dropping axles and losing them, or maybe it simply snapped or stripped, regardless, we have them available. The titanium axles won't affect play, but you'll know you have one, and that's cool. Maybe you can brag to your friends about it.
Note: If you use a titanium axle with a titanium yoyo, it's possible that they can merge together and bond. Because of this possibility, we don't recommend using a titanium axle with a titanium yoyo. It's not our fault, it's just science.