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This is called a King but does not seem to be of royal bearing - no King tuning slide system. King sousaphone bell has a distinct bulbous shape that I do not detect here. It's hard to tell with sousaphones, but it looks like a bigger body too. At least you get what appears to be a King 18 mouthpiece (which are excellent).

http://www.ebay.com/itm/Sousaphone-Fibe ... SwnH1WW21S

1st valve slide makes it look Holton. Is this likely? And if so how are Holton fiberglass sousas, I'm only getting spotty references in a search. Bloke hates them, that's all I can tell.

Hmmm.... King neck but odd-looking valve caps. The lower mouthpipe is not typical King.

I think this is a Holton sousaphone. The King upper mouthpipe is compatible with Holton sousas.