Review on 🔩 YVSPTIK 2020 Series M4 T Slot Nuts - Roll-in Spring Ball Loaded Elastic Nuts (20 Pack) Carbon Steel for 2020 Series Aluminum Extrusion Profile Rail with 6mm Slot - Ideal for 3D Printer by Jason Unruh

These T nuts fit my 4040 and 4080 aluminum extrusions well and I prefer this type with a ball to hold them in place which is especially useful when installing vertically. They stay in place pretty well and I haven't had any issues with the 8mm threads. They come in a small pack of 20 and I have not found any defective items in the pack. Good price for 20 of these and they can take a lot of torque without breaking when used with quality socket or pan head screws. I use them on a full spec racing sim frame that gets a lot of movement and heavy use and they hold up well.