The actual dimensions of my M6 Nut are 10 x 11.25 x 4.90. In the design there are bigger, to ensure just enough tolerance for easy incertion of the nut. You can adjust those with the Parameters NutWidht and NutHeight.

The Nut chamber is closed with 0.2mm layer on the top, so you need supports only for the wings.

There is also "Open" version, with a smaller dimentions for the nut, for press fit.

The Fusion360 files are also here.