What’s the proper name for the wavy metal washer some manufacturers use to hold the movement in the case?

Can someone help with the right term to search for, a name for those ghastly wavy metal washers some manufacturers use to create compression when the caseback is screwed on? When squished between caseback and spacer ring, it holds the movement securely in the case.

I have one where it is missing and someone has stuffed little clippings of insulated electrical wire to provide the necessary friction. If there are generics about I'd be happy to cut and bend to size.

[ATTACH…

What's the proper name for the wavy metal washer some manufacturers use to hold the movement in the case?