Cafelat Silicone Group Gasket - 9 mm Nuova Simonelli
71 mm x 56.5 mm x 9 mm (Blue) conical. For the Nuova Simonelli Aurelia and Aurelia II, as well as the Victoria Arduino Adonis and Black Eagle models. The Cafelat and "NS 1" side faces up when installing.
Some product history and notes:
Seem to last longer and hold a tighter seal than the standard issue Gaskets that come with the machine.