In my line of business (automotive repair) we have "throw away" bolts for certain applications, especially for head bolts on certain engines. They are a one-time use item because they are tightened to a "Torque to yield" specification where you first tighten to a lower than nominal tension, then another 90 or 180 degrees of rotation to preload the bolts against further stretch and compress the head gaskets. You CAN re-use these bolts, but it is highly recommended by the manufacturers that they be replaced.

This is just one example of bolt "failure" or a bolt developing questionable second-time use characteristics because of initial over-tightening.

The same is true for ANY bolt. I guarantee that I can snap off a brand new 10-32 or 5mmx.8 thread bolt by merely tightening it with a T-handle, and the bolt will not break in the thicker shank area, but in the threaded area directly adjacent to the material it is being screwed into. That being said, it is silly to tighten any bolt that tight in our applications. The desired procedure is to pre-tension the bolt so that a maximum of bolt "stretch" is achieved without permanently changing the bolts length. This is possible because steel is mildly elastic, and will allow a small amount of "stretch" or pre-load without incurring permanent physioligical change. However. . "stretch" these bolts, with the focal point for that stretching, and eventually they will work-harden that small area and it will become brittle or start to fatigue. When THAT happens is when you will start seeing failures during tightening of the bolts, but it is highly unlikely that a bolt will fail (unless grossly over tightened) while the engine is running. That little game still belongs to non-preloaded bolts that have not been tightened properly, and are basically moving around a bit and developing rapid fatigue stress in the localized area next to the screwed into material (prop hub). It doesn't take very many cycles to develop a failure mode, in this instance.

Best bet. . tighten the prop bolts TIGHT, and worry about breaking them from overtightening them the next time around if you change props or have to take the current propellor off. Even better is the use of a torque wrench, but it's still not totally possible to make sure you have enough bolt "stretch", although, in theory, torquing to a known "proper" value is much better than not getting there at all.