Flange Accomodations are different type.

International standard use PN, ANSI and JIS. Pressure Number (PN) are from Europe standard. American National Standards Institute (AISI) stands for standard from America. Japan Industrial Standard (JIS) are from Japan.

They all have different size. But they stand for Outside diameter size, bolt circle diameter, bolt size and flange thickness. Beside size, they also stand for materials used.