Most people use the cross wrench used for the glow plug to also tighten the prop nut. I did that for years also. After having the nut occasionally come loose, I now use a 10 inch adjustable wrench. That is too much wrench, so you need to learn how to use it. I have NEVER had a problem since I made the change. I also stopped using the plastic spinners and instead use the large nuts that a started rubber cone can grasp. No more problems.