King medium bore trombone

[JanStortelder]

Hello, yesterday, I bought an old King Tenor trombone with serial number 31217 for the reasonable price of 60 euro’s (which is, as the trombone has some holes, an unloosenable tuning slide (in my bare hands, that is) and a lacquer of which I do not know if it is meant to be gold or silver). I can’t find any information on its bore, except for the slide, which says it is a medium bore.
Nowadays, this would mean it would have a .525 inch or 13.33 mm bore, but back then, bores were smaller, so I don’t think those rules apply.
Does anybody know what bore this trombone has?

[BGuttman]

If that serial number is right this is a VERY old trombone (>100 years old). Does it not have a slide lock or bell nut? If it does, the serial number is wrong. Also, a trombone with this serial would have a double brace (1 straight and 1 curved) under the mouthpiece.

100 years ago Medium Bore would be 12.7 mm or so (this is Conn's #3 bore).

You can get a rough idea of slide bore by measuring inside the stocking; especially if this is a 100 year old horn with soldered on stockings. If the stockings are drawn (i.e. made from the same piece of metal as the inner slide) then all bets are off for this measurement.

[JanStortelder]

Thank you very much for your fast reply!
I have measured the bore, it is a 12.7 mm bore.
I am also rather certain about that serial number, it is on all parts of the instrument and the trombone doesn’t have a slide lock or bell lock, though it doesn’t need any of that.