Hello,  This is in answer to Alan Rigg's question on main spring
length.  I have replaced many main springs over the years in music
boxes and I still don't like it.

You cannot always trust the length of what was in there due to others
cutting it short because of the eye tearing out of the end of the
spring or it broke and someone just cut a new eye hole in it.  However,
to find the correct length, here is the formula and it's accurate.

  Spring length for barrel

I.D. of spring barrel squared X .7854
O.D. of the arbor or center clutch X .7854
Then subtract those answers: O.D. from the I.D.
Divide by 2
Divide by thickness of spring material
Length is in inches
Divide by 12 for footage.

Example:

  5.0" I.D. spring barrel
  1.0" O.D. arbor
5 x 5 x .7854   =  19.635  square inches
1 x 1 x .7854   =    .7854
Subtract        =  18.8496
Divide by 2     =   9.4248
Divide by .035" = 269.28 inches (Material thickness is .035")
Divide by 12    =  22.44 feet
Now have fun installing it.

Works every time.

Have a great day,
Ralph Schultz