colour:SilverMaterial:aluminum alloysize:21*13*7.8mm3030 M8 T Slot Nuts for 3030 aluminum extrusion with 8mm slot, use for T-slot aluminum profile 30x30 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 3030 extrusion or 3030 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).3030 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.Package Contents:30*3030 Series NutsOnly the above package content, other products are not included.Note: Light shooting and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.