# Why “58mm” isn’t one standard > Two machines can both be 58mm and still not take the same basket. What the number measures, why border diameter decides fitment, and which series you need. Source: https://espressofit.com/guides/58mm-is-not-one-standard/ --- “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. ## A basket has three diameters, not one Pick up a filter basket and you are holding three separate measurements, and only one of them is the number on the box: - **Tamper diameter** — the inside of the basket at the top, where the coffee gets compressed. This is the “58mm”. It decides your tamper, and nothing else. - **Body diameter** — the outside of the basket wall. This decides whether the basket drops into the portafilter at all. - **Border diameter** — the outer lip at the rim, the part that actually rests on the portafilter and is held by the retaining spring. **This is the measurement that decides whether a basket seats correctly**, and it is the one almost nobody publishes. IMS is the exception: it publishes border, body and tamper diameters for every basket, and it organises its whole Competition range by *border* diameter 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](https://espressofit.com/guides/ims-basket-codes/). ## The series, and what each one actually measures | Series | Border Ø | Body Ø | Tamper Ø | Sold as | | --- | --- | --- | --- | --- | | [**B70**](https://espressofit.com/baskets/series/b70/) | 70 mm | 60 mm | 58/58.4 mm | [58mm](https://espressofit.com/standards/58mm/) | | [**B68**](https://espressofit.com/baskets/series/b68/) | 68 mm | 60 mm | 58 mm | [58mm](https://espressofit.com/standards/58mm/) | | [**B64**](https://espressofit.com/baskets/series/b64/) | 64 mm | 58 mm | 57 mm | [57mm](https://espressofit.com/standards/57mm/) | | [**B62.5**](https://espressofit.com/baskets/series/b62-5/) | 62.5 mm | 54 mm | 53 mm | [54mm](https://espressofit.com/standards/54mm/) | | [**B60**](https://espressofit.com/baskets/series/b60/) | 60 mm | 52 mm | 51 mm | [52mm](https://espressofit.com/standards/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. ## The same number, two different baskets These are the machines in this database that each series is cross-referenced to, taken straight from the entries: ### B70 — Ø70mm border (21 machines) - [Breville Oracle](https://espressofit.com/machines/breville-oracle/) - [ECM Estetika](https://espressofit.com/machines/ecm-estetika/) - [ECM Mechanika MAX II](https://espressofit.com/machines/ecm-mechanika-max-ii/) - [Flair 58](https://espressofit.com/machines/flair-58/) - [La Marzocco GS3](https://espressofit.com/machines/la-marzocco-gs3/) - [La Marzocco Linea Micra](https://espressofit.com/machines/la-marzocco-linea-micra/) - [La Marzocco Linea Mini](https://espressofit.com/machines/la-marzocco-linea-mini/) - [Lelit Bianca (PL162T)](https://espressofit.com/machines/lelit-bianca/) - [Lelit Elizabeth (PL92T)](https://espressofit.com/machines/lelit-elizabeth/) - [Lelit Kate (PL82T)](https://espressofit.com/machines/lelit-kate/) - [Lelit MaraX (PL62X)](https://espressofit.com/machines/lelit-marax/) - [Lelit Victoria (PL91T)](https://espressofit.com/machines/lelit-victoria/) - [Rancilio Silvia](https://espressofit.com/machines/rancilio-silvia/) - [Rancilio Silvia Pro](https://espressofit.com/machines/rancilio-silvia-pro/) - [Rancilio Silvia Pro X](https://espressofit.com/machines/rancilio-silvia-pro-x/) - [Rocket Espresso Appartamento](https://espressofit.com/machines/rocket-appartamento/) - [Rocket Espresso Epica](https://espressofit.com/machines/rocket-epica/) - [Rocket Espresso Giotto Fast](https://espressofit.com/machines/rocket-giotto/) - [Rocket Espresso Mozzafiato Fast](https://espressofit.com/machines/rocket-mozzafiato/) - [Rocket Espresso Porta Via](https://espressofit.com/machines/rocket-porta-via/) - [Rocket Espresso R Nine One](https://espressofit.com/machines/rocket-r-nine-one/) ### B68 — Ø68mm border (2 machines) - [Gaggia Classic GT](https://espressofit.com/machines/gaggia-classic-gt/) - [Gaggia Classic Pro (E24)](https://espressofit.com/machines/gaggia-classic-pro/) 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. ## Where we hold a strict line 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. ## Group parts don’t follow the number at all 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](https://espressofit.com/guides/groupheads/) and [the E61 group](https://espressofit.com/guides/e61-group/). ## What we can’t tell you yet 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. See [how we verify](https://espressofit.com/methodology/). ## So what should you actually buy? Match the *series*, not the number. Look your machine up in the [parts finder](https://espressofit.com/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. ## Sources 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](https://espressofit.com/baskets/ims-b70-competition-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](https://espressofit.com/baskets/ims-b68-competition-1-cup/) (“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. --- From EspressoFit — a sourced espresso parts compatibility database. Every fitment claim on this site cites the manufacturer page it was verified against, with the date it was read. See https://espressofit.com/methodology/