15 x 4 x 4mm. EPDM rubber, 80 Shore Hardness. For Astoria and Wega, this gasket is held in place with a tiny fixing nut. They are usually quite brittle when they wear out, and must be pried (and likely chipped) out of the gasket holder with a sharp tool. They are then installed in any position/fashion.
Attention CA Residents: Prop 65 Warning
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.