Fast Ace AS-01's and DHZ "GPX" forks have a 20 mm bore in the RHS leg ... They use an axle that's 20 mm on one side and steps down to 15 mm ... Basically the right side of the axle doubles as as a built in wheel spacer and another spacer is fitted on the LHS to space the disc right with the caliper ... When you tighten the axle nut up the wheel is bolted to the LHS fork leg only and the 20 mm spacer/axle floats in the RHS fork leg ... When two allen head screws on the fork foot are tightened , the leg clamps tight to the axle ... They're designed that way to prevent the fork legs from being pulled in towards each other out of parallel thus avoiding "stiction" , stiff movement , blown seals and inner fork damage ...
The "standard" straight axle which clamps everything together is actually an F'wit of an idea engineering wise ... Take a good look at ANY hydraulic ram system on Earth moving equipment etc and you'll see that both ends of each ram floats freely on pins ... IF they were bolted solid they'd stuff up in next to no time at all ... All metal structures flex ... The smart engineer knows that and makes allowances for it ... the dope "engine ear" blindly bolts everything up rigidly then blows seals , seizes and scores rams and can't understand WHY ...
Anything that slides HAS to be be precision aligned to function correctly and provide the maximum service life ... since a wheel has to be held rigidly ... the only alternative is to come up with a system that keeps the slider centre to centres floating free while the wheel is tensioned ... then locks the axle in place while maintaining the precise c to c of the fork legs ...
When standard set ups are loosened and re-tightened several times ... the spacers and alloy fork feet tend to get crushed or impacted ... that in turn puts the operating c to c out ... Same goes for rear shocks ... heaps are broken or blow seals because they're not allowed to float and find their own "happy" spot ...
Honda forks usually have hardened steel inserts cast into the fork feet to prevent c to c variations over time ... and the wheel and axle spacers are all precision made to a certain size ... You can stuff a set of forks up simply by fitting new wheel bearings that aren't the exact same width as the stockers ...
