I tried searching for these, couldn’t find any, so you have a link?They are quite useful iirc, they sit over the boss and help hold the brakes on (I think), had some LX brakes where they broke and I seem to recall at some point realising I could slide the brakes off over the bolt on the rear. It was many years ago.
You could find some, I think there are repro ones in metal sold for the m900 brakes.