This piece is meant to be used to allow smooth linear motion in a light duty cnc or printer.
I designed this based on a method I saw somewhere on the web for mounting 608 bearings to a piece of angled aluminum. If i remember where i saw it i will update with a link. The idea is that you turn a square tube 45 degrees, and this will roll along the top of it. You could also use a piece of angle iron too, laying on its hypotenuse. There are mounting holes that allow you to mount something on top of it. I have not printed this yet as I am still awaiting a heated build platform. Comments are welcome as this is my first thing.
Image is of the Angle aluminum version. The advantage of printing this is you get precisely positioned holes, and a flat surface on top with mounting holes.
Print this out. Note, it will be upside down, if that isn't obvious.
You could however use 2 per slide, one above and one below the square tubing, although you'd also need another bracket of some sort to connect them.
You will need 3 608 bearings, 3 8mm bolts and 6 8mm nuts. Assemble so that there is a nut on each side of the piece, spacing the bearing away from it. I have included an STL with the bearings drawn in to give a better idea of how it should be assembled. Again i have not yet printed this so I am not sure exactly what length bolts would work best.