Swartchild Black Shield Mainspring #440791 for 16s South Bend No. 17528 - Steel

Swartchild Black Shield Mainspring No. 440791 for 16s South Bend 1st model movements, Factory No. 17528, 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.