The brewing groups which La San Marco has used their own design of brewing groups over the years. This is quite unique, seen a lot of espresso machine brands use a standardized E61 style of brewing groups. For this reason they can also use their own design of portafilter, the one with the 3 ears.
There are in total 4 brewing groups used by La San Marco. That are the Lever brewing groups, where the pump pressure is generated with springs inside the brewing group. The groups used in the San Marco 85,95,100 and 105, these do have a lot of similarities. But will have sometimes small differences. Then you also have the manual groups, these run on pump pressure but have a mechanical system inside the brewing group. So you won’t find a solenoid valve on these groups.
The advantage of using the same type of brewing groups on their espresso machines is that a lot of the parts are compatible with each other. On all the brewing groups you can use the same portafilter gasket, 64x52.5x5.5mm, and the same shower screen of 48mm