Cafelat developed the ingenious design sometime back. The bottom of the portafilter is removable, allowing for use as a standard spouted portafilter or a bottomless portafilter.

The key to this portafilter is having the bottom plate fit in and out using a press-fit silicone o-ring. The o-ring has been custom made to provide enough grip to hold the plate firmly in place and also allow the plate to be removed without too much fuss.

Another neat feature of the spouts is that they always line up in the correct position and are held firmly in place with a simple grub screw. The allen key for the screw is included with a portafilter set. These come with a spring for the basket, but the basket itself is NOT included (your existing basket will work just fine). Made from 304 stainless steel.