The Trangia Simmering ring comes with all Trangia stove and pot sets, and it's the only moving part in the burner assembly. So, given the endlessly long lifespan of the Trangia spirit burner, it's a good thing they offer it as a spare part... cos it's the only part that is likely to give up the ghost after decades of use.

The Simmering Ring gives you flame control by dropping it over the top of the Trangia burner, so you can boil water or simmer your laksa, and it packs away neatly inside the cooker assembly.