[walkman]

Not sure if this is the correct place for this but...

In several places on my aircraft I have NPT rather that AN style fittings. This includes the primer nozzle which isn't really a primer nozzle just a male AN male NPT fitting, also on some of the fittings tee-ing off MAP line for gauge and ECU.

I realize that with AN fittings it's the flare, not the thread, that seals. That isn't true with NPT which I understand uses a tapered thread as the seal.

Should I use pipe dope on the NPT threads anywhere to ensure a correct seal?

 

[Mel]

I've been using Permatex #2 form-a-gasket for about 50 years on all NPT threads. Never had a problem. Doesn't take much.

 

[Neal@F14]

Ditto on the Permatex brown goo.

Probably the very best stuff that exists to use on NPT taper thread fittings.

I use the Aviation #3 Form-a-gasket myself because.... well I have a giant sized bottle of it that'll probably last a lifetime. The only differences between the #2 and #3 formulas is the percentages of talc or kaolin, vegetable oil, and pine rosin in the mixture. The #3 is a lot more runny, but if you leave the bottle opened in a hot Texas hangar for a couple weeks, it'll solve that problem