These are custom made OpenBuilds Tee Nuts. They were designed to slide into slots with less hassle than the standard rectangular tee nuts. They have angled corners to allow for a smooth transition.
OpenBuilds Tee Nuts fit V-Slot and most aluminum tee slot extrusion that has at least a 10mm wide tee nut slot.
Please check the dimensions if you are using another type of extrusion.
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