... But not adjustable during cooking, because the tubular rivet connection between base and cover much is too tight. To bring something to the boil and then simmer to continue is not possible unless you take the hot Adjusters from the burner, adjust the cap with pliers and snippets on again. The thing is absolutely useless for me.
The burner of my ancient fondue sets has two handles, one for holding the burner pot, the other to adjust the air supply; The latter is totally facilitated consistently.