This is part of my Baby-Huey large format 3D printer project. It may also be of use for other projects.

Huey is a work in progress so the assembly has never been used in earnest.

It was printed and assembled and seems to do what is it is supposed to do.

This thing uses 4 skate bearing to travel along a 25.4 (or 25mm) square tube.

It is not stable until it is attached to its mates and all four are supported by threaded rod (M6 but imperial might work).

Stepper motors or idler pulleys can be fitted to two sides.
The steppers are mounted via an adapter plate.

The round shaft is 12mm.

I've changed to a simpler two bearing thing and have no plans to use this part any more.