You can easily use the feature of body to create the nut with the fillet as the above figure
Answered with a tutorial: https://grabcad.com/tutorials/how-to-create-a-nut-with-curvature-on-the-top-or-bottom
There are two more ways to do that.
- Revolved cut along the profile with the mid-point of the hexagon edge.
- Extrusion with draft (or taper) and then subtracting it.
thanks it works