4040 M4 T Slot Nuts for 4040 aluminum extrusion with 8mm slot, use for T-slot aluminum profile 4040 series. Spring ball loaded makes these T slot nuts sit and stay where you want them,and don't slide around while your trying to screw into them.It was so much easier than fiddling with the stock T nuts that refuse to lock in place correctly.You can insert and remove these T slot nuts easily. If you work with T slot extrusions,these are a must have.These T slot nuts fits perfect on 4040 extrusion or 4040 rail with lots of different components on your rail.For you to mount something else. If you also lost pieces to your printer and need replacement, they fit nice and secure in rails.Use them to add new brackets to stiffen the frame on your 3D printer (Tevo Tarantula). Carbon steel :All high quality carbon steel construction,high hardness.Nickel-plated surface, rust resistance.4040 Series Aluminum Profile T-Nuts widely Use to build CNC routers, 3D printers, CNC laser cutters, CNC plasma cutters, robotics projects, 3D carvers, machine guards, workstations,and more. Easy to be roll into T slot of aluminum profile.