MFU Driver Technology

Onyx has been a pioneer in hub technology for years. The patented sprag clutch mechanism offers ride characteristics, performance, and robustness no other mechanism can. On top of that and nearly limitless colour options, Onyx hubs have arguably the best freehub/driver mechanism around. 

Read further to learn why that is! 

High Level of Modularity

Since 2020 Onyx has supplied all their Classic and Vesper hubs with MFU assembly. The three-letter acronym stands for modular freehub unit. It’s a brilliant piece of engineering since it creates a level of modularity across the whole product lineup that isn’t seen anywhere else!

All the Classic and Vesper hubs employ the same freehub body – or the driver as it’s called. Thanks to the clever engineering done at Onyx HQ, one can use the same freehub body for Classic hubs equipped with downhill-specific 110x20mm / 157x12mm sizing and Vesper hubs that would be suited to gravel duties in 100x12mm / 142x12mm specification.

Installation is as simple as it can be. The driver employs a press fit style of assembly and is held in place by the end cap/widget. Simply pull the end cap off and perform the same manoeuvre with the driver. Installing the driver is done the same way but in the opposite manner. 

No Need for Else

The true beauty of the MFU axle design manifests itself when the need arises the move on from one freehub interface standard to another, say from Sram XDR to Shimano Micro Spline or the other way around. The only part that needs replacing is the driver itself – and in some cases the end cap. No need to replace axles and bearings with them and perform a full teardown of the hub in the process.

The Shimano HG, and Sram XDR drivers share the same end cap/widget whilst the Shimano MS driver has a dedicated one. In the latter case, the end cap is clearly marked with the text “Micro Spline”. 

If the need arises to replace the end cap with the driver, it’s best to make sure that it’s of the correct model. End caps for 12mm thru-axles are supplied in two versions: regular and +3.5mm version. The end cap model depends on the axle sizing. Refer to the schematic table below.

End Cap ModelStandard version+3.5mm version
MTB, road and gravel135mm142mm
MTB141mm (“Boost QR”)148mm Boost
MTB150mm157mm Super Boost
MTB & Fatbike170mm177mm

It comes quickly apparent that the +3.5mm end caps add 7mm to the axle length.

Do note that exceptions might present themselves in certain cases. For example, the end caps might differ between the Centerlock and the ISO 6-bolt shells. If in doubt, ensure that you are about to order the correct one.


Since the introduction of the MFU axle design, Onyx Racing Products hubs only been supplied with the Sram XDR driver. This has been a source of confusion from time to time since the majority of mountain bike cassettes employ the XD standard.

Conveniently, the XDR can be converted to XD with the use of a 1.85mm thick spacer that’s supplied with all XDR-equipped hubs.

In Summary

MFU axle design is an expression of clever engineering that brings several benefits. Among them are a highly functional and robust design. The modular design makes all drivers cross-compatible with each other which makes the move from one interface to the next a breeze. 

Disassembly and installation require no tools – a feature that makes the MFU a truly universal design. 

Older hubs can be upgraded to the current MFU axle design. The list of needed parts includes the driver, axle, end caps/widgets and the lockring.