Click on the button Insert rectangle. Later the rectangle's width is the cap nut's height and the rectangle's height is the raw body for half of the hexagon (pay attention: not width across flats is meant, but the hexagon's outer radius.

Raw body due to the fact that the hexagon has to be cut from it via sketch 2. The height has to be a little bit wider than the hexagon's outer radius.

Hexagon with inner circle = width across flats and outer radius (width across flats ~ 0.866 * hexagon's outer radius)

Based on the origin, drag out a rectangle with width = H and height = S/SQRT(3) + 0.1. (So the height is a little bit more than the outer radius of the hexagon.)

Determine the base line as Rotation axis.

Click on the button Create parallel line.

Select the base line and set the parallel with a distance of DK/2 (DK = cap nut diameter).

Click on the button Radius with 2 elements.

Determine first and second line and afterwards the rough position of the circle segment. In the dialog box, set the radius to DK/2 (DK = cap nut diameter).

Click on the button Create parallel line.

Select the left side as base line and position the parallel with a distance of M (M = hexagon height).

Click on the button Create parallel line.

Select the rotation axis as base line and position the parallel with a distance of S/2 (S = width over flats).

Click on the button Create parallel line.

Select the rotation axis as base line and position the parallel with a distance of DW/2 (DW = Outer diameter of contact surface).

Create outer chamfer at hexagon: Rotate selection

Create second outer chamfer at hexagon: Copy and rotate selection

With the use of the functions Trim elements to each other, Delete element and Trim element with other, remove all needless lines.