[DanEC]

I don't use split washers without a flat washer under them to protect the component surface - even in OEM applications that may have omitted a flat washer, I add one. I would not be surprised to learn that a flat washer further increases the chances of loosening when there is a lot of vibration. I now use blue loctite more than I used to - but on any aluminum component I rely on anti-sieze and a lock washer and figure I will have to re-tighten them later.

Interesting thread.