After a few props got lose on me at starting(a few also came off) I concluded I was not tightening them enough. I had always used the small prop cross wrench also used to tighten the glow plug. I believe most people use this wrench to tighten the prop also. I have a very large and strong hand but I was still not tightening the nut enough because that wrench is too small for tightening the prop nut. Using a torque wrench occasionally is not a bad idea. Of course, I do not know what torque to tighten it to. Now I use a 10" adjustable wrench. An 8" is the size I would purchase, but I had an extra 10" wrench so it is now part of my flight tools. I tighten it very tight. I do not recall having a problem since.