The 1/8-27 is known otherwise as "1/8" Pipe". It has a tapered thread, and requires some type of thread sealer to prevent leakage. I prefer to use a flexible, non-hardening sealer like Permatex Super 300. It was developed in the 1950's to seal aviation gasoline fittings, and it works better then the Permatex 3D, which is also a non-hardening brush-on sealer. It's best to avoid Teflon pipe tape on gas like fittings, as slivers of the tape can get into the fuel system and clog carburetor passages or keep float valves from working properly. The most common adapter fitting for fuel lines has a 1/8" pipe male thread, and a 1/4" or 5/16" "inverted flare" on the other end.
Jerry
