Can we wash our bikes like pros?

[SadieKate]

There's a crush washer in my 105 cassette. As I said, it's extremely thin, maybe half again the weight of heavy-duty aluminum foil. It goes under the "wavy" lock ring.

We're looking directly at an XT cassette. Between the lock ring and the 1st cog (both of which have serrated or knurled edges - what you call wavy?), is a washer. It is made of paper thin steel and is slotted into the threading of the lock ring and it is not meant to be removed.

We don't think of it as a crush washer. It is not thick enough or designed to deform. If you try to pry one off, it will behave like spring steel and it looks like chrome-plated spring steel. It returns to shape when messed with.

I think if it was meant to be replaced everytime you removed the cassette, Park Tool or Shimano would tell you to do it. And Shimano absolutely loves to sell you bits and pieces like chain pins. Not ones to shirk from making an extra penny.