This is a carriage was made to be used with 623 bearings for those that have these and don't want to have to buy linear bearings. Perfect for all those varying sizes of rods that you got from those printers and scanners ; ) I drew the design in google sketchup. This is iteration 24. It functions quiet well. You may need some nuts to hold the screws in place, but I found that the holes were tight enough on most prints. Btw, the bracket in the picture was an earlier version that still required a washer. The current design doesn't need it.