Does a 3/4" FIP gas fitting effectively reduce the run size for 1" CSST?

Question

I'm running about 50' of 1" CSST natural gas tubing and want the best flow possible before I branch out and step down. I see there are two choices for connections;

1" MIP (3/4" FIP) x 1" CSST
or
1" FIP x 1" CSST

If I select the first fitting, am I effectively reducing my entire 1" tubing run to 3/4" since it can fit 3/4" MIP threads even if I used the 1" MIP side of the fitting?

Saying it another way, does fitting number two have a better throughput than the first regardless of how I connect the first?

Answer 1

I think you would need to look at the inside of each fitting to determine this. In gas adapter fittings, it's not unusual to see a 1" MIP fitting also be internally threaded for 3/4" (and 3/4" MIP fittings internally threaded for 1/2"). Obviously such a fittings have slightly smaller internal diameter than a pipe of the same size, due to increased wall thickness required for the internal threaded bore; however, such fittings often have a restriction that's even smaller at the bottom of the bore.

They are not intended to be considered in capacity/flow calculations because they are typically made for use at the end of the line, and line sizing calcs would take them into account. Most gas appliances have regulators/restrictions/orifices that are smaller yet. Your question seems to imply that you need max flow, so one would assume an alternative (non appliance) use which you did not reveal.

I think the solution is to visually inspect the two components, or upsize the entire line so the concern is moot.