In the past it was standard that a espresso machine had a flange on 1 or on both sides of the boiler. Nowadays this becomes rarer and rarer. The flange on a boiler can nowadays only be found on the heating element side.
You have 2 types of boiler flanges, the casted ones and the pressed ones. The boiler flanges which are casted, for instance with Gaggia and Vibiemme espresso machines don’t require boiler rings. With the pressed sheet metal ones, for instance on the Faema E61 espresso machine, a aluminium boiler ring is required to spread out the force of the bolts and not deform the soft copper.
The advantage of having a boiler flange on one side is that the cleaning and inspection of a boiler was a lot easier then with just a heating element hole.
The early models of Faema used a double flange system on their boilers. You would have a heating element flange and a water level flange. These flanges had a gasket to seal off the boiler. To spread the pressure equally over the gasket a inner and outer ring are placed. This ring prevents the deformation of the copper boiler flange and side flanges. Over...