I don't know if there is one answer to that one ...
Seems they used whatever was available at the time .... they "Farmed Out" on these and other pieces ...
I have ones that are .... strips (3 and 4), individuals, butterbean shaped, oval shaped, metal buttons, celluloid buttons, etc ...
For replacements ... I have been successful with "Martin Vintage Butterbeans"
http://www.elderly.com/accessories/items/GTM28.htm
They required a tiny enlargment of the hole in the headstock ... I used a small round file ... maybe 5 "passes" with the file ... and also an adjustment in the mounting holes (of the tuners) ...
I am very paranoid about my Bakelites ... but I never felt that they were in danger by making these small alterations ...
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My Steel Shoes Site
[This message was edited by Rick Aiello on 15 January 2003 at 06:09 PM.]