It's the single most common fitment mistake: someone buys a "standard" 58mm basket, tamper or bottomless portafilter for a Breville and it simply won't seat. The reason is size. Breville home machines use a 54mm portafilter — not the 58mm commercial standard that La Marzocco, Rancilio, Lelit, Gaggia and most prosumer machines share. Four millimetres is the whole difference between a part fitting and not. (A few of Breville's commercial-style machines are the exception — more below.)
Breville's portafilter is 54mm, a size essentially unique to Breville among common machines. In the UK and Europe these exact machines are sold under the Sage brand — same machines, same model names, same 54mm portafilter — so everything here applies to the Sage-badged equivalents too. A 58mm basket is 4mm too wide to drop into a 54mm portafilter, and a 54mm basket rattles loose in a 58mm one; there is no adapter that makes them interchange.
Only parts made for the 54mm format. The good news is Breville publishes its own OEM sizes clearly, so the fitment is well-documented. On the basket side, the main choice is single-wall vs dual-wall (see single- vs dual-wall baskets) — both in 54mm. For a tamper, you want a 54mm tamper, not 58mm.
Each links to its page with the portafilter size and every basket and part confirmed to fit it — or start from the Breville brand hub or the 54mm standard page.
Breville Dual Boiler, Breville Oracle, Breville Oracle Dual Boiler, Breville Oracle Jet and Breville Oracle Touch use a 58mm portafilter instead — built around a commercial-style group rather than Breville's 54mm home format. So for these, standard 58mm baskets and tampers are what you want. Everything else in Breville's home line is 54mm; when in doubt, check the specific machine's page rather than assuming.
Every size here is quoted from Breville's own product and parts pages on each entry. See how we verify compatibility, or the portafilter sizes guide for how 54mm compares to 58, 57 and 52mm.