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A group gasket is specified by three numbers in this order: outside diameter, inside diameter, and thickness, all in millimetres, and you must match all three. The thickness is the one that changes how the portafilter sits, which is why shim spacers exist: Seattle Coffee Gear lists a 0.8mm gasket shim for $0.99 precisely so you can correct a handle that has drifted too far round. Gaskets themselves are cheap, from a $2.97 flat gasket up to about $9.95 for a Gaggia group gasket.
How gaskets are specified and priced
| Spec | What it means | What happens if it is wrong |
|---|---|---|
| Outside diameter | The measurement across the outer rim | Too small and it drops into the group, too large and it will not seat |
| Inside diameter | The hole the basket sits inside | Wrong bore fouls the basket rim and causes drips |
| Thickness | Usually between about 7mm and 9mm | Handle sits too far round or too far back |
| Profile | Flat or conical | A conical gasket in a flat group leaks |
| Material | Rubber or silicone | Rubber hardens faster, silicone stays pliable longer |
| Shim spacer | 0.8mm packer sold separately, $0.99 | Corrects a handle that has crept past centre |
Example prices: La Marzocco 7mm flat gasket $2.97, Nuova Simonelli flat group head gasket $5.50, Rancilio group head gasket $4.25, Gaggia group gasket $9.95, per Seattle Coffee Gear and Whole Latte Love listings checked August 2026.
Read the handle position, not the calendar
A new gasket puts the portafilter handle somewhere left of centre when it is locked. As the rubber compresses and hardens, the handle travels further round. Once it is past centre and heading right, or you have to lean on it to get a seal, the gasket is done. That is a better indicator than any interval, because water hardness, shot volume, and how hot the group runs all change the rate.
The other tell is a drip or a hiss from the edge of the group during a shot, which people often misread as a portafilter fault. Rule that out with fix a leaking portafilter first.
Measuring yours without guessing
Pull the old gasket, wipe it dry, and measure with calipers if you have them: across the outer edge, across the bore, and the height. Write the three numbers down in that order, because that is how sellers list them. If the old gasket is badly compressed the thickness reading will be short, so cross check against the machine manual or a parts diagram for your model, and buy the thickness the maker specified rather than the thickness of a flattened part.
If the handle sat too far round even on a fresh gasket, that is when a 0.8mm shim goes in behind it. If it sat too far left, you need a thinner gasket, not a shim.
Silicone versus rubber, and the fitting mistake
Silicone gaskets stay pliable much longer and come out easily at the next change, which is the main practical argument for them. Rubber is cheaper and is what most machines ship with. Neither changes the taste of the shot. The genuine mistake to avoid is fitting a new gasket over the top of the old one, which happens more than you would think on machines where the old gasket has sunk into the group recess. Get a screwdriver or a gasket hook in there, confirm the recess is empty, then press the new one home evenly all the way round.
Do the shower screen at the same time; it is off anyway. Prices and choices are in shower screen cleaning.
Order by the three numbers
Search with your machine name plus the size. Buy a spare while you are there, because the second change always arrives sooner than you expect.
Related reading
- Espresso machine gasket kit
- Fix a leaking portafilter
- 54mm vs 58mm portafilter
- Coffee gear guides hub
FAQ
How do I know what size group gasket I need? Measure three things on the old one: outside diameter, inside diameter, and thickness, in millimetres. Sellers list them in that order. Check the thickness against your machine manual, because a worn gasket measures thinner than it started.
Why does my portafilter handle point to the right now? The gasket has compressed and hardened, so the handle travels further round before it seals. That is the standard signal to replace it, and a 0.8mm shim can correct the position if a new gasket still sits too far round.
Is a silicone group gasket better than rubber? It stays pliable longer and is much easier to remove at the next change. It does not change how the shot tastes. Rubber is cheaper and is what most machines ship with.
Repair or replace: the free repair or replace calculator weighs the part cost against a new machine before you order anything.
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