Holley inlets are SAE inverted flare fittings, not NPT fittings. Regardless of what Earl's may or may not call them. the difference is National Pipe Thread, NPT, seals with the threads becasue the plug is tapered. SAE Inverted flare fittings seal by holding a double flared steel line in compression against the inverted flare inlet fitting. They are a straight thread, not tapered. If you installed a NPT to AN fitting into a Holley, you did damage it. but it isn't that bad, you can buy replacement inlet fittings from Summit or any good speed shop.
Droptop is right regarding NPT fittings that you thought you had, sealers will help and it shouldn't take many threads before a NPT plug seals. However Holley carbs don't use NPT threads in the inlets. Inverted flare fittings should never be installed with any kind of sealer, if they don't seal, something is wrong with the metal to metal seats. this includes all fuel lines and brake lines using SAE inverted flare fittings. Same can be said for any flare fittings, sealers should never be needed or used. If it leaks you've got another problem, the threads aren't the sealing surface for any flare fittings. They do make a conical flare metal crush gasket to help seal flare fittings that may be slightly misaligned or scratched. Seco Seal is one brand of these.
Hope this helps,
[This message has been edited by SY1 (edited 07-19-2002).]