[davepl]

There are several types, as you note. It's quite possible that Willie is using a style intended only to prevent galling, and that has nothing to do with sealing. That's why I asked for the RO or part number early on to look it up instead of guessing.

I think the best answer is "it does both" but there are only certain applications where it's is appropriate as a sealant.

95% of the people using it on the threads have no idea that the seal is from a 45 or 37 degree tapered flange and not the threads anyway! Other than where your pipe nipple screws into the intake manifold for your heater hose... not many places.