If you've ever had an item on your bike that just seems to always come loose, you'll be interested in these little gems. The 2-part lock washer uses ramps cast into the opposing faces to prevent bolts or nuts from coming loose. In fact, vibration will tend to make the connection tigher, not looser, making these possibly the best lock washers that you'll find.
I used these on my highway pegs, which seemed always to turn a bit when I pressed on them. One pair on each side, placed next to the part (bolt or bracket) which was getting unscrewed by my foot pressure, and they no longer move. I could have used two Nord-Locks' on each side to be really sure, but you should know that once torqued down it becomes very difficult to loosen the bolt. It would pay to leave one side with a normal lock washer so you can remove the bolt later if you desire.