The axles and freehubs are interchangeable between all the Spin Doctor Pro rear hub models,(Note: Although they are not cross compatible with the original Spin Doctor parts). This interchangeability allows customisation of the Spin Doctor Pro hubs to suit your needsSpin Doctor Pro Solid Axle:Rear - M10x135x185mm with bearing covers and axle nuts. Weight: 140g.Spin Doctor Pro 12mm Axle Coversion:Several riders have asked Halo to offer a 12mm T-axle hub. So, rather than building a whole new hub from scratch, we have devised a simple and cheap conversion kit to allow a 12mm T-axle to be used with our Spin Doctor Pro hub.This means that all of our Spin Doctor Pro hubs and wheels that use Spin Doctor Pro hubs can easily and cheaply be modified to fit yet another configuration of frame. (and if you change your frame, you can easily run the QR or 10mm axle option again).Includes - service axle, bearing spacer and 2 push-on CNC alloyend caps. 12mm T-axle not included (this should be part of the frame).Spin Doctor Pro Axle Parts Kit:Includes: CNC alloy end caps, Freehub spacer, Fits Standard 135mm QR axleSpin Doctor Pro QR Rear Axle Kit:Direct replacement rear alloy axle - for Spin Doctor Pro Hub, QR Type, includes dust covers.Spin Doctor Pro Solid Axle:M10 x 135 x 200mm extra long chromoly axle with bearing covers and axle nuts.Weight: 148g.