“58mm” is the most-quoted number in espresso, and it is the one that causes the most returns. It is genuinely useful — it tells you which tamper to buy, and it correctly rules out the 54mm Breville line and the 52mm La Pavoni levers. But it is not a complete fitment answer, because 58mm describes the tamper, not the basket seat. Two machines can both be 58mm machines and take baskets that are not interchangeable.
Pick up a filter basket and you are holding three separate measurements, and only one of them is the number on the box:
IMS is the exception: it publishes border, body and tamper diameters for every basket, and it organises its whole Competition range by borderdiameter rather than by tamper size. That is why an IMS code starts with the border figure — B70 is a Ø70mm border, B68 is Ø68mm. See the full code breakdown.
| Series | Border Ø | Body Ø | Tamper Ø | Sold as |
|---|---|---|---|---|
| B70 | 70 mm | 60 mm | 58 / 58.4 mm | 58mm |
| B68 | 68 mm | 60 mm | 58 mm | 58mm |
| B64 | 64 mm | — | 57 mm | 57mm |
| B62 | 62 mm | — | 54 mm | 54mm |
| B60 | 60 mm | 52 mm | 51 mm | 52mm |
Read the first and fourth columns together and the point of this page falls out: B70 and B68 are both sold as “58mm”. Same tamper, same body, two millimetres of difference at the border — and that two millimetres is the whole fitment question.
These are the machines in this database that each series is cross-referenced to, taken straight from the entries:
Every machine in both lists is a 58mm machine. A tamper crosses freely between them. A basket does not, and IMS keeps the two lists separate on purpose.
IMS itself is not perfectly consistent here, and we would rather show you the conflict than paper over it. Its Competition catalogue heads the B68 series“B68 (BORDER Ø 68 mm) CARIMALI, GAGGIA, LA CIMBALI” — Gaggia is a B68 brand. But IMS’s own Gaggia compatibility page answers a different question differently: “most IMS B70 series precision baskets fit the standard 58mm Gaggia portafilter.”
Two sources from the same manufacturer, two different claims. We follow the catalogue, so no B70 basket in this database is cross-referenced to a Gaggia machine. The reasoning: the catalogue’s series assignment is a precise engineering statement about border diameter, while “most … fit” is a hedged answer on a marketing page — and the cost of being wrong is someone buying a basket that will not seat. If IMS publishes a per-model B70→Gaggia statement, we will revisit it and say so.
Shower screens and group gaskets fit the grouphead, not the portafilter. An E61 machine and a Gaggia Classic are both 58mm and take completely different screens — 60mm for E61, 55mm for the Gaggia GA series. Those parts are keyed by group in this database rather than by size, for exactly this reason. See groupheads explained and the E61 group.
There is a fourth dimension to portafilter fitment — the ear or lug spacing, the tabs that lock the portafilter into the group. It is why a portafilter from one 58mm machine often will not twist into another 58mm group, even though every basket dimension matches.
We do not publish ear geometry, and we are not going to estimate it. Essentially no manufacturer prints the figure, and a spec column that sat empty for almost every machine would imply a precision this database does not have. Where it matters, it is written into the entry prose from a source we actually read. If a manufacturer starts publishing it, we will add it and cite it — the same rule as everything else here. Seehow we verify.
Match the series, not the number. Look your machine up in theparts finder and buy from the baskets confirmed against it; every one of them carries the manufacturer page it was checked against and the date it was read.
The border, body and tamper figures above are quoted from IMS’s Competition Series catalogue and its per-product pages, each read firsthand and dated on the basket entry that cites it — for example the B70 2 Cup H26.5 (“Border: Ø 70 mm”, “Body: Ø 60 mm”, tamper “Ø 58/58.4 mm”) and the B68 1 Cup H24.5 (“Border: Ø 68 mm”, “Body: Ø 60 mm”, tamper “Ø 58 mm”). The Gaggia conflict is quoted from IMS’s Competition catalogue and its Gaggia compatibility page, both cited in full on those entries.