If it is original equipment, the nut should match the shaft, and it will be a heavy duty one piece threaded nut. If it is a replacement wheel, it may have an insert, which could be either threaded into the nut, or fit into a star shaped cut out on the back in the nut. YouTube is your friend, try to figure out what brand you have. Search Edson steering wheel removal, and Lewmar steering wheel removal for a start. They both look like what you are showing of yours.