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Today I did a cleaning on my Thermo Pride furnace with a Beckett burner; it had been a few years since I'd done a full cleaning of the combustion chamber by removing the oil gun, so I did that this time.
There is a mineral wool "collar" on the front of the Beckett's burner tube, where it goes into the ThermoPride's inside combustion chamber, and it was brittle and cracked as the burner assembly came out. It is held on the burner tube by two clips that are a welded on part of the burner tube.
What do you call this mineral wool collar on the burner tube, and where can I get one?