I've stretched the jaws on a few wrenches by using the open end, particularly backwards. Knew it would happen beforehand, but you gotta make due with what you have when in the field.
Take it with a grain of salt if you will but I was using the open end for a turbo to manifold bolt that a socket can't fit onto and a closed end wouldn't fit on. Had to use an Gear Wrench open ended 14mm which just opened up as I tried to loosen it. Decided to just drop some cash and bought a Craftsman wrench set and used their 14mm. Didn't let go and I was able to loosen the bolt.