Aluminum linear stop for MGN12 linear rails to mount parallel to typical 2040 frame extrusion found on 3d printers and DIY CNC’s. Mounting Linear Rails and Alignment: In this linear rail installation we align the carriages and rails. Rail Parallelism is importance for precision and smooth motion or movement in prevent linear motion binding. The two rails on the WorkHorse 3D Printer are used in parallel while some unnecessary load can result if the carriages are not mounted a range of parallelism. If you’re building the large DIY WorkHorse 3D Printer you’ll have to maintain the dual x-axis lead screws synchronization. For More Information See https://3ddistributed.com/product/mgn12-24-linear-rail-alignment-tool-carriage-stop/