Print two of these blocks to align a linear rail exactly centered on a 2020 extrusion. It is designed for MGN15 rails. These are the dimensions for building RatRig printers, they use MGN15 and Openbuilds-compatible 2020 extrusions. They will also help with other printers with these dimensions.

Keep in mind: When mounting 2 rails on an axis, this tool is fine for screwing in the first rail (sometimes called Master) nicely centered. The second rail needs to be screwed in so the assembly runs smoothly. Don't simply screw both rails with the alignment tool!