Cafelat Silicone Group Gasket - 8.5 mm E61
73 mm x 57 mm x 8.5 mm (Blue) suitable for all variations of the E61 group, this is the thicker of the two for worn groups and/or portafilters where the portafilter locks into place too far to the right. The Cafelat and "E61 8.5" side faces up when installing.
Some product history and notes:
Great price and service from Espresso Parts. Will shop with them again.