About this 3D model

I really like Greg Frost's most recent x-carriage but I had a couple ideas that I thought might make it more accessible. Changes: 1) Added back the other two pairs of mounting holes found on the Prusa sled. 2) Moved the belt clamps in so as to not block the zip-tie slots. 3) Added a bit more width to the belt clamp slots to accommodate slightly wider belts. 4) Made the M3 hole in the tensioning stud a bit tighter & deeper.