The Trangia spare
 screw cap for spirit stoves, with rubber washer. If not using the simmering ring, it can be used 
for extinguishing the burner, but first remove the rubber washer from 
inside the cap as this may melt when extinguishing the burner. (Note, do
 not screw the burner cap on tightly to the burner whilst the burner is 
still warm, as when it cools down the cap will become very difficult to 
remove).