Why inner and outer threads on Petromax stove fuel cap

I recently bought a Petromax stove.

I noticed that it has threads on the top of the fuel fill cap. Why?

 

Can we have a photo of the stove?


Tony

 

@esarratt
One of these?




These aren’t threads, they’re just circumferential grooves to provide a grip when unscrewing or tightening the cap.




The internal threads on the cap however take the stove’s keeper plug …




… that occupies the burner vapouriser mounting boss when the burner’s removed while the stove’s stowed for travel.



John

 

Got it. Nice! Thanks!

 

Oooops! Sorry. I just realized that I put this on the wrong forum. I belong to the classic camp stove forum too.

Here are a few pics of my new-to-me stove.

 

I also own two Petromax No.100 stoves. They are from 1959 and 1963. On these,the filling screw is knurled.

 

Grand old stoves.