This is a simple T-slot nut based on the design by Manfred Morgner. I significantly refactored his original OpenSCAD script. It should be easy to generate usable parts any aluminum extrusion size with a variety of hole sizes. I've included a sample output that fits the 30mm extrusions that come with the Prusa i3 MK3(S+).

Update 2022-03-05: add the option to include a nut. By default it should fit an M3 hex nut from the Prusa kit. However, please note that you will need to print with supports if this option is enabled. Set Nut_Height=0 to disable.