Hey makers and builders! If you're working with 2020 series aluminum extrusions (you know, the 20mm x 20mm profile), you're gonna need these T-nuts. This pack comes with 100 of them, so you've got plenty for your project. They're M4 thread size (so they fit M4 screws/bolts), made from carbon steel with a nickel plating. The cool thing about these 'drop-in' or 'post-assembly' T-nuts is that you don't need to take your frame apart to install them. Just drop the nut into the T-slot anywhere along the profile, and when you start screwing in your bolt, the nut turns sideways and locks into place. Super convenient for adding parts later. Perfect for 3D printers, CNC machines, robot frames, workbenches, and all kinds of DIY projects. Dimensions are about 10mm x 6mm x 3.5mm with a 6mm neck width. A must-have fastener for any aluminum extrusion system.