In this tutorial we will be drawing N M12x1.75 hex nut.
We use the following sketch as reference
The dimensions are in mm.
For starters, draw a hexagon on the front plane by using the polygon sketch feature in solidworks
Click on the polygon tool and create a hexagon of 18 mm & 20.78 as shown in the sketch.
To dimension the sketch click on dimension tool and click on two parallel sides and enter the distance as 18 mm. The final sketch will be as shown in figure.
Now go to the features tool bar select the extrude tool and extrude the current sketch to a distance of 10.80 mm. Select the midplane option so that the body is extruded equally on both sides of the sketch.
Now click on the front face and draw a circle of 16.60 mm in diameter.
Now exit the sketch and click on extruded cut feature. We are going to remove the material from the hexagon at 30 degree draft.
Select the circle as profile to remove material and make sure you check the flipside cut option. Enter 30 degrees as draft.
The nut should look like above when you select the extruded cut and enter the parameters as shown in figure. Now click ok. Got to features tab , click on mirror feature and 
Select top plane as plane to mirror and select the extruded cut as the feature to mirror.
Click ok and the feature will be mirrored. Now create a circle of diameter 12mm on one of the hexagonal faces and create a extruded cut as above throughout the nut.
Now you have to create a create a spiral & use swept cut to create a thread in a nut.
Hint: User helical spiral, and take pitch as 1.75mm and height of spiral as 10.8 mm and use a triangular profile of .5mm of size to create a thread. I leave it to you as an exercise. The final nut after doing all of above will be like
