NPT means national pipe taper. The fittings on your gas line are likely 1/8 or 1/4 NPT The thread pitch is 27 threads per inch and they are tapered in order to make a seal as the fitting is tightened. I suspect your fittings are 1/8 pipe. your barbed fitting should have 1/8th pipe threads on it where it screws into the tank. I think 1/4 threads would be too big. Without seeing the hole in the tank where the fitting goes I am only guessing. I hope this helps. You could buy both sizes and use the one that fits. Good luck.
Weeds
