Anyone know what this washer is for?

[LemonHunter 583]

Was floating around under the valve cover.

[M3AN 4016]

Size (scale)? Material? Vehicle?

 

[LemonHunter 583]

E36 328 Motorsport

I can't for the life of me find my vernier or a ruler. 

According to my measuring crescent though its about 18mm OD and about 12mm ID. 

It was chilling down by exhaust valve 12.

Under what I think is called the cam carrier or cradle? 

[Gabe79 410]

What does your valve cover gasket look like? That looks like the o-ring for spark plug holes on the valve cover gasket.