Thanks Jon,
This is a subject that concerns us all and I for one always have something new to learn. It is also one of the biggest problems I come across. My all time favorite being 3/8" bolts in M10 holes and always in the most inconvenient and hard to access place. Second is wrong tensile rating and not torquing to correct tension or stretch followed by incorrect and/or mismatched bolt heads/ nuts. Dodgy anti-vibration control is up there too.