What is the correct wrench size for a 3" 150 flange?

The correct wrench size for a 3" 150 flange is 1-1/16". This size aligns with the standard bolt sizes used for a flange of this type. For a 3" 150 flange, the bolts typically have a nominal size of 5/8" and, according to ASME B16.5 standards, the required wrench size for a 5/8" bolt is indeed 1-1/16".

Using the appropriate wrench size ensures that you can effectively tighten or loosen the bolts without damaging them or the flange. Other sizes listed, such as 2-1/2", 1-1/4", and 3/4", do not correspond with the specifications for the bolt size on a 3" 150 flange configuration, making them unsuitable choices for this specific application.