Jeepboy.
There should be a nut on the outside also. A lot of people don't use them, myself included. The reason I don't use them is, if your tire is slipping on the rim, it is hard to tell that this is happening until the tire and tube moves so much that it can tear the tube at the valve stem.
If you don't use the nut, you can tell that the tire is moving on the rim because the valve stem will start bending over at an angle. This gives you time to fix it before it tears the tube.
Modern tire locks work pretty good to keep the tire from moving, but, if you run low air pressure, the tire can still move on the rim.
Just my $ .02