Schott flanges are available in five sizes, shown in the chart below. They are called out by their nominal inside dimensions in millimeters. The three configurations shown in the photo below are standard off-the-shelf components: flat flange, flat flange with a domed top (as a lid), and flange with o-ring groove. Typically, a vessel will utilize one o-ring flange with either a flat flange or a "domed" or "lid" blank flange.
|DN size; nominal ID, mm||Flange OD, mm|
Many configurations are possible, including custom machined interfaces.
Plasma chamber w DN150 flanges
of Schott DN flanges
The orings are called out in meteric sizes and are available in several material choices, including viton, silicone, and teflon encapsulated silicone. An o-ring compatability chart can be referenced here.
A stainless steel wraparound toggle clamp holds the flanges together, with an o-ring between the mating parts. This photo shows how the shape of the clamp conforms to the shape of the glass flanges.
The flanges are rated for one atmosphere of differential pressure, either full vacuum or internal pressure.
crossectional view clamp/flange interface & red silicone oring
On the right is an example of  a custom interface between a DN200 Schott flange component and a base machined from teflon utilizing the Schott clamp. This approach can be used for a "head" as well.  In addition to teflon, stainless steel is an alternative material interface, and can be machined to provide drive support and vessel porting.
Click on the image on the right for a profile view.
The photos below show a custom glass vessel utilizing DN200 flanges. An all glass "head" is constructed on a DN200 "lid", and a DN200 o-ring flange is fused on a 100L round bottom flask.