Small animals tend to live shorter lives than larger animals. There are a few theories as to why that is, but the one I believe is most popular is: small animals tend to live shorter lives anyway (because of threats from predators), so there are fewer opportunities to evolve to be long-lived.
The American National Standards Institute (ANSI) Class 150 is a system of dimensional standards for weld neck, threaded, slip-on, lap joint, socket weld and blind flanges. Dimensions for facing, bolts and studs are also included in ANSI Class 150. ANSI Class 150 establishes measures for pipe sizes.
Mistakes sometimes occur because cast iron or ductile iron flanged fittings have 250 cast in them (indicating a 250 PSI pressure rating) but the flange dimensions and bolt pattern conform to ANSI/ASME B16.1 Class 125 (or ANSI/ASME B16.42 Class 150). These will not bolt to an ANSI/ASME B16.1 Class 250 flange.