The group head gasket is the most common pieces that wears on an espresso machine. Silicone is longer lasting than NBR rubber.
Coffee experts prefer silicone gaskets because of the greater compressibility, better seal and easier portafilter locking.
The light grey color makes it much easier to spot coffee grounds that need to be cleaned.
Silicone doesn't stick to the shower screen when it ages.
Three grooves make it easy to get a removal tool in.
The top side is marked UP so it's easier to know which direction to put it in for a correct seal.
Fits the DE1 and most E61 machines.