http://www.huashuoflange.com/slip-on-flanges/
EN1092-1 is the British flange standard, 11 is the 11-type flange, B1 is the flange sealing surface model, DN50 is the nominal diameter, PN100 is the nominal pressure, and 6.15 is the flange S wall thickness.
Flange, also known as flange flange or flange. Flanges are the interconnected parts between shafts and are used for the connection between pipe ends; they are also used as flanges on the inlet and outlet of equipment for the connection between two equipment, such as reducer flanges. Flange connection or flange joint refers to a detachable connection in which flanges, gaskets and bolts are connected to each other as a set of combined sealing structures.