What is the appropriate wrench size for a 1-1/4" 300 flange?

For a 1-1/4" 300 flange, the appropriate wrench size is generally 1-1/16". This size is used because it accommodates the specific dimensions and tolerances associated with 300-pound forging flanges, which typically require a slightly smaller wrench than the nominal size of the flange itself.

Choosing a wrench that matches the nominal pipe size, like 1-1/4", would not provide the correct fit, as the flange faces and the associated nuts are designed to work with a specific measurement that allows secure tightening without damaging the flange. A wrench size larger than necessary, such as 1-1/2" or even 2", would also not fit properly and would risk stripping the nut. Thus, using a 1-1/16" wrench ensures compatibility and effectiveness in engaging the nut on the flange, allowing for proper torque application and maintenance of integrity in the connection.