Serrated washers on brake callipers

[Fifelad]

I thought I was going mad while fitting new mudguards on my Dolan Preffissio I noticed that on both my rear and front brake callipers that there is not a serrated washer but just a “normal “ washer. I may have dropped one when callipers have been off but it seems a coincidence that both callipers didn’t have them. What is the actual point in the serrated washer anyway ?

 

[classic33]

To try and avoid parts being shaken from where they're fitted. Also to prevent the but nut coming loose

 

[midlife]

Often replaced by nylock nuts to stop loosening?

 

[Fifelad]

Cheers for the replies