A dosing funnel (dosing ring) sits on the rim of the portafilter to guide ground coffee into the basket without spilling over the edge — especially useful with the Weiss Distribution Technique (WDT). It is chosen by the portafilter's outer diameter so it seats on the rim, so funnels are size-specific: a 58mm funnel for 58mm machines, a 54mm funnel for Breville, and so on. Many use magnets to snap onto a steel portafilter.
New to sizing? See espresso portafilter sizes explained, or browse all part types.