How to fix this leak?

[LI-er]

Hi, thanks in advance for any assistance.

I recently purchased this whip to fill my pony bottles from a larger cylinder. I only used it a few times but I've had it for several months.

Now it's leaking from the fitting (see the arrow). I removed the debris shown in the close up picture of the fitting with a cotton swab and tried wrapping the threads with of the male fitting with teflon tape, and cranking down the tightening nuts as much as I can but it didn't have any effect on the leak. Doesn't seem like an O-ring goes in there.

Pictures include the whip, and both sides of the fitting.

 

[Valerii Vakshul]

There needs to be a gasket, O-ring.

 

[happy-diver]

Mismatched fittings, how many threads are you able to use, check for burrs, tighten it really tightly, or not
Metal to metal is fine, if you have enough thread coverage and it seals which it seems to have been doing

My electric booster has some metals to metals

with no psssssssssssss

 

[LI-er]

I don't understand where the O-ring would go, given that it's a flange (like a round cone) where the two pieces couple together. If it goes on the outside of the flange, how would that help as the metal fitting doesn't screw down that far.

 

[Valerii Vakshul]

I don't understand where the O-ring would go, given that it's a flange (like a round cone) where the two pieces couple together. If it goes on the outside of the flange, how would that help as the metal fitting doesn't screw down that far.

Perhaps your smooth cone has a different radius than the mating seat.
You need to go to a hydraulic transition and hose store. They will find the transition you need there.