Not really a Caesar related question.... I assume you want to specify branch fittings or types.
You might consider: Is a welded fitting (tee) required / available for header / branch sizes ? Need for reinforcement.... pressure limitation will govern. Type of reinforcement .... sifs differ. Welding requirements .... material dependent, also butt weld required or is a fillet acceptable ? Inspection needs ... for example is x-ray required ? Client / owner preference. Cost of course.