Swartchild Black Shield Mainspring #4375½ for 0s South Bend No. 32528 - Steel

Swartchild & Co. Black Shield Mainspring No. 4375½ for 0s South Bend movements, Factory No. 32528, steel, new in envelope. See images for further details. I specialize in hard to find watch parts and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.