So what’s the difference between ‘bolt through’ and QR, when discussing these axles?
Broadly, one’s supposed to be quick release, generally with a cam, while the other actually involves bolts, of either the allen or hex variety.
In practice, though, the Maxle is designed to be a quick-ish release system, to give you the strength of a 20mm through-bolt in a package that you can actually access on the trail.
Personally I settled for a 9mm through-bolt. On a standard 9mm QR you’ll notice the actual ‘bolt’ is really skinny, and doesn’t fill the axle, hence can flex quite easily. 9mm through-axle, like RWS or Superstar’s versions, swaps that relatively skinny bolt for one that fills the dropouts – and is 9mm thick. It’s probably not as good at resisting twang as something 20mm or 15mm thick, but it’s a start, and it fits my existing forks.
As for 20mm vs 15mm, it seems to be just a competing standards thing – Rockshox started with 20mm, Fox with 15, although I think they’ve kinda settled on 15mm now.