3030 M8 T-Slot Nuts for 3030 Aluminum Extrusion with 8mm Slot, use for 30x30 Series T-Slot Aluminum Profiles. The spring loaded ball allows the T-slot nuts to sit and stay where you want them, and not slide around while you try to screw them in. This was so much easier than dealing with the stock T-nuts that refuse to lock properly. You can easily insert and remove the T-slot nuts. If you are working with T-slot extrusions, these are a must have. T-slot nuts fit perfectly on the 3030 extrusion or 3030 rail with many different components on your rail. So you can mount something else. If you also lost parts from your printer and need to replace them, they fit well and are secure in the rails. Use them to add new supports to strengthen the frame of your 3D printer (Tevo Tarantula). The 3030 series aluminum profile T-nuts are widely used to build CNC routers, 3D printers, CNC holographic cutters, CNC plasma cutters, robotics projects, 3D sculptors, machine guards, workstations, etc. Easy