How does this brake calliper securing nut arrangement work?
IIRC, the cover slides off by pulling on it, the two locknuts are locked against each other to adjust the caliper play (usually with the goal of creating as little slop as possible with no binding of the arms), and then the cover is pushed over the two locknuts. I believe the idea is its got lots of little notches inside so it can grip both nuts at once, making it impossible for them to vibrate loose.