I'm looking at building a wooden or possibly an aluminum cnc router. But some of the basics are rather confusing to me, one of which is the styles of linear rails/bearings. For example: Aluminum bars with standoff blocks on each end, and a bearing in the center. 15pcs Optical Axis Guide Bearing Housings Aluminum Rail Shaft Support Screws Set CNC Parts Squarish bar with a linear rail. MGN12 500mm Linear Rail Guide with MGN12H Block CNC Tool Supported linear rail with a bearing. SBR12 800mm Supported Linear Rails Shaft Rod With 2pcs SBR12UU Block Bearing Which is the best? is there an ideal design, provided tolerances are same across all 3?