[ David Dewey wrote in 150612 MMDigest:

> The damper brass plates have the damper spring inserted into them
> ...  The old Schaff number was 539 ...

If Schaff still has #518-1/2 Kimball butt plates, then buy those.
Use a drill press with a machinist's vise to hold them.  Drill a hole
in the proper place using a numerical drill bit.  Finding a chuck to
hold those really small bits can be a challenge.

You can buy the damper springs 0.029" or 0.033" wire as part no. 538.
A number 69 bit is 0.0292" diameter but finding good ones is tough.
A number 66 bit is 0.033" so use the next size larger size bit which
is #65 at 0.035".

They used a dab of solder to hold the spring.

Don Teach