# The E61 group, explained > What the E61 group is, why it means a 58mm portafilter, and how to tell if your machine has one — plus every E61 machine in the database. Source: https://espressofit.com/guides/e61-group/ --- If a machine's spec sheet or a forum reply says it has an **"E61 group"**, that single fact tells you a lot — including its portafilter size. Here's what the E61 is, why it's shorthand for 58mm, and how we treat it on this site. ## What the E61 group is The E61 is a **brew group design** — the chromed, angular head the portafilter locks into — introduced by Faema on its E61 machine in 1961 (named for the solar eclipse that year). Its defining trick is a **thermosiphon**: water continuously circulates from the boiler through the heavy brass group, keeping it at brewing temperature so the metal itself stabilises the shot. It also gives a mechanical **pre-infusion** as you lift the lever. Because the design was never patented into exclusivity, dozens of manufacturers build machines around an E61 group to this day. ## Why "E61" implies 58mm The E61 group is built to the **58mm commercial portafilter standard**. So when a maker states a machine has an E61 group — even if the spec sheet never prints a portafilter diameter — the 58mm size follows from the standard. That inference is exactly how we handle these entries: the manufacturer confirms the E61 group firsthand, and 58mm comes from the E61 standard rather than the maker's own page. Because that last step leans on the standard, not a manufacturer's printed number, we mark these entries **"measured"** rather than manufacturer-verified — an honest, documented inference rather than a firsthand spec. See [how we verify](https://espressofit.com/methodology/) for what the confidence tiers mean. ## How to tell if you have one The tells: a tall, chromed, angular group head bolted to the front; a shot that starts on its own as the machine reaches temperature (the pre-infusion); and a maker's spec that names "E61". If your machine has an E61 group, any 58mm basket, tamper, shower screen or group gasket made to the E61 standard is your starting point — though group parts (screens, gaskets) fit by the group itself, so check [groupheads explained](https://espressofit.com/guides/groupheads/). ## E61 machines in the database (6) - [ECM Estetika](https://espressofit.com/machines/ecm-estetika/) — E61 (58mm) - [ECM Mechanika MAX II](https://espressofit.com/machines/ecm-mechanika-max-ii/) — E61 (58mm) - [Rocket Espresso Appartamento](https://espressofit.com/machines/rocket-appartamento/) — E61 (58mm) - [Rocket Espresso Giotto Fast](https://espressofit.com/machines/rocket-giotto/) — E61 (58mm) - [Rocket Espresso Mozzafiato Fast](https://espressofit.com/machines/rocket-mozzafiato/) — E61 (58mm) - [Rocket Espresso Porta Via](https://espressofit.com/machines/rocket-porta-via/) — E61 (58mm) All are 58mm — see the [58mm standard](https://espressofit.com/standards/58mm/) for every basket and part in that format. --- 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/