Referred to as the "GASKET FOR DOUBLE POD EPDM 90 Sh[ore]", 55 mm O.D. x 45/50 mm I.D. Pictured upside down. You will still need to keep both your original group head gasket installed as well as this one. The dispersion plate screen holder slips inside this, the screen goes onto the plate, and the screw goes through all, affixing the assembly to the group head.
WARNING: This product can expose you to chemicals including lead, which are known to the State of California to cause cancer, birth defects, or other reproductive harm. For more information, go to www.p65warnings.ca.gov.