Bialetti - Spare Rubber Seal - Replacement Part Suitable for Mukka Express Cappuccino Maker - 2 Cups bialetti original replacement rubber seal/ring/gasket suitable for the mukka express 2 cup cappuccino maker. outer diameter 8.0cm/3.1in - inner diameter 6.0cm/2.4in. loose packed cup size is based on espresso cup sizes and not on regular tea or coffee cup sizes.