Think of how a jet is made. Widest part at top, that takes more room in main hole, nest step on rod is smaller, less taking of hole and more gas, you get the last step
I think we are talking two different things. I get the steps on the rods.
Jet has home that has a cross section area of 1 ( just numbers here) then you put a rod down the center with a cross section area of 0.5, effective cross section area of the combo is 0.5.
The next step the cross section area of the rod is 0.25 so effective combined cross section area is 0.75 etc.
I was saying that in the FSM they call out main jets that are 120-310s then if you want to lean out the carb "one-step" you use jet number 120-294s and if you want to go one more "step" lean you go to jet number 120-297s
