The group gasket (grouphead seal) is the rubber ring seated inside the grouphead that the portafilter clamps against to seal under brew pressure. It is a wear part — as it hardens and compresses with heat and use, the portafilter starts to sit slack or the group weeps during the shot, which is the classic sign it is due for replacement. Unlike baskets and portafilters, a gasket is keyed to the grouphead, not the portafilter diameter, so it is matched by machine/group rather than by a 58mm-style standard.
Gaggia’s own part is “8.5 mm thick and made of black rubber,” and Gaggia states it fits “the Gaggia Classic Pro and all semi-automatic espresso machines with an EF0030A boiler” — so it is cross-referenced to the Gaggia Classic Pro here (Gaggia’s part number 11004543). It does not fit the pressure-profiling or lever machines in this database, whose groupheads seal differently. Verified against Gaggia’s official parts page on 2026-07-13.
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