How to identify your "Stencil" C-Melody saxophone
currently 'in progress', please use what there is externally.....
http://www.saxpics.com/infonmisc/stencils.htm.
http://www.drrick.com/stencil.html
(and)
           
http://www.cybersax.com/QA/Q&A_Topic_Directory.html 
Note : on the
Cybersax site,  scroll down to the 'Stencil Saxophones' link  
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more details at - http://www.cmelodysax.co.uk/saxophones/question-answer.htm#stencil - until this page is completed
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This isn't foolproof - just a handful of 'features' which are common to a particular manufacturer are shown below
- but, BEWARE, all stencils didn't necessarily have all the features, some were reserved for the 'named' saxes.
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Stencils cannot normally be dated from lists of manufacturers serial numbers - they don't correspond,
( To my knowledge, no specific lists of stencil serial numbers have survived from the 20's....)
First, the 'Big Three' stencil makers.......
Buescher
Conn
Martin
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And the rest, by no means inferior, but they just didn't produce copious amounts of stencils
King