Gooseneck washer

[dbbd]

The washer separating metal from metal in our gooseneck was torn.
What is the name of this washer? What material is it made if? Where do I buy a replacement?

Thanks
Dan

[Tafika II]

What mast system? Mine is stainless steel on a Selden rig. Can't tell you the size of the washer since we don't know what mast & boom you have.