There are various brewing groups used on Bezzera espresso machines. There is no line clear line with brewing groups used on commercial or domestic models.
On a lot of the commercial espresso machines there is a solenoid valve operated bell group head. This brewing group uses a portafilter gasket 72x55mm. this group head is used on Bezzera models such as the B2000, B2006, B2009, B6000, Ellisse and the Galatea.
The other type of brewing group is the E61 style of brewing group. This type of group head is used on domestic as well on commercial models. This is a manual group and not solenoid valve operated This group head uses a portafilter gasket with a OD of 73mm and a inner diameter of 57mm. these can be found on the Bezzera Magica, Galatea and the Unica.