NO!!! You don't want to chase the threads on the fuel tank, especially if you don't know and understand threads. If you or someone else has already mucked up the tank port with the incorrect tap, or cross-thread the sediment bulb intake port, the tank is likely ruined. Attempting to 'band-aid' fix it is suicide. Do you want to be nervous every time running the tractor worrying about if the fuel is going to leak? NPT Threads are TAPERED. They are different than standard UNC and UNF threads. 3/8 isn't the nominal OD size like on a standard 3/8-24 UNF thread where .375" is the MAJOR DIAMETER of the nominal thread size. 24 designates threads per inch (TPI). On a 3/8 NPT thread, the 3/8 is defined as the minor diameter of the pipe or tube the thread fits. When an NPT tap is screwed in, the deeper it goes, the larger the top of the hole becomes, it's tapered small to large, and if screwed in too far, will destroy the hole size completely. The purpose of an NPT thread is to tightly seal the connection. As the male part is screwed into the female part, it naturally creates its own seal at each revolution. If it is enlarged beyond the largest portion of the tap, then the hole is ruined. There are GO-and NO-GO thread gauges for NPT threads just like standard UNC and UNF threads. If your 'new' sediment bulb is not going in, be aware that some mew/aftermarket units are junk out of the box -I've had one in my life, and if not careful they can ruin your tank. It matters where you buy parts from. Also related to the fuel line and sediment bulb is the special thread size used on the 1/4" steel line, fittings, and ports, both on the sediment bulb and the carb brass inlet elbow. The thread is a special pitch, used on brake and fuel lines, 7/16-24 UNS and anything else used will only booger it up and cause leaks. Forget Teflon tape, silicone, or any gasket material.
Tim *PloughNman* Daley(MI)