In other words, it's stuck on the outside of the portafilter. This design makes it much more flexible and easier to use than other products. It also makes the coffee bed flatter. One more thing, while we use high quality aluminum alloy to make the espresso funnel lighter, not as bulky as stainless steel, we have also drilled the funnel with 8 strong magnetic magnets to help the portafilter funnel securely attach securely to the espresso portafilter and won't fall off easily.
