I need to add NPT fittings with 5/16" nipples to the Carter street fuel pump I just bought. How do I know if I need 1/4" NPT or 1/8" NPT? The pics on Jeggs look the same. Is the difference the diameter or the pitch/coarseness of the threads? I don't even know what NPT stands for, but I do know it is a non gasketed interference fit.

Scott B. "I'm a self-made man... I started with nothing, and I still have most of it!" 68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph 69 340 GTS stock 14.18@ 95.60 mph 01 5.9L Ram 1500 Quad Cab 4x4 01 3.5L 300M 16.23@ 86.97 mph