This is a silicone gasket for a Bialetti 6-cup moka pot. It's slightly thicker than the original rubber gasket, so it won't tighten to the same position as when using the original. However, there's no problem with its use. Original gaskets deteriorate and need to be replaced regularly, but silicone gaskets are durable, so replacement might not be necessary... I bought a pack of 8, but I don't need to replace them, so I'm selling them. I've been using one for over 5 years (see photo 3), and it's stained coffee-colored, but it works perfectly fine. Size: Outer diameter 73mm x Inner diameter 55mm x Thickness 4mm (actual measurement)