So simple, there isn't even a "C" to this one. Understand how to tell the difference between "A" and "B" torch fittings, as well as the difference between fuel and oxygen connections.
"A"-style fittings have 3/8" threading.
"B"-style fittings have 9/16" threading.
Fuel fittings are left-threaded and tighten to the left. They are standard-marked with a groove (notch) on the screw nut.
Oxygen fittings are right-threaded and tighten to the right. They are standard-marked with a smooth screw nut (no notch).