Does anybody know what is this spacer

[TBandy]

IIs this spacer for movement or dial ?

[Marc]

I've only ever seen those used in case backs to push either the movement, or more commonly the movement ring forwards towards the crystal to hold things nice and snug when the back is screwed in place.

[Klassiker]

It looks like a spring washer to take up the play between a case or caseback and the movement.

[TBandy]

1 hour ago, Klassiker said:

It looks like a spring washer to take up the play between a case or caseback and the movement.

Sounds logic to me, I had not thought of it