Hex shaft

[Joe G.]

It sounds like you don't need a hub, but just standard bearings. The simplest solution is probably to press fit something like this into your chassis rail. If you don't have the machining capabilities to press fit bearings this way, use something like this with the correct bore, and swap the bearing. Alternatively, you could use standard round bearings, and turn the ends of your shaft to a round profile.

Another consideration is, you don't necessarily have to support your shaft with your chassis rail. If your gearbox provides adequate support for your shaft by itself, you can just drill a clearance hole into the chassis, and let the gearbox's bearings do the work for you. It is almost never a good idea to support a shaft with more than two bearings, as this can cause binding.