La San Marco无底Portafilter

In some cases bottomless portafilters are interchangeable between brands, such as the Nuova Simonelli bottomless portafilter, this one is interchangeable with the one used on most Victoria Arduino espresso machines. This has to that it is the same brand.

You can add any filterbasket to the bottomless portafilter. But in most cases a deep double filterbasket is installed. This has to do that there is no bottom in the way.

In almost most cases bottomless portafilters are made from brass which has been chrome plated. A few brands make bottomless portafilters from stainless steel. But that is a minority

Bottomless portafilters start as regular casted portafilters. But during the machining process the bottoms are cut out of the casting, which creates a bottomless portafilter. After this the portafilters are sanded and polished into a mirror finish and chrome plated.

No, the portafilters used on Breville, Sage and Solis espresso machines are unique to those brands. And are also a lot smaller then the standard 58mm portafilters, which are used for instance on E61 brewing groups.