Does anyone know the white alloy, mainspring part number, for an 18s Keystone Watch Co. dustproof model? Thanks.

Brian, I am working on a dustproof now and replaced the mainspring from my stock with a white steel "Super Security Brand". The package label reads;

802
21 x 1-1/2 x 20
T-END
FAC #2190
18s NYS

This works fine in the s/n331779 dustproof I am restoring

Thanks Dave,
I have two other company white steel mainsprings and the packages say, M/S #2190, 20x1x20 T end. Was the spring you took out of the Keystone a 20 or 21 wide? I haven't taken my watch apart yet.

Brian, I did not mike the width so it was whatever came out of the bag. If you have a white steel that is 20 instead of 21, that may be all of .2 mm (0.008") narrower and should work fine.

Thanks Dave, I figured it would be fine, if I wind up needing a mainspring.