Newall Security Mainspring #904 for 12s South Bend No. 55528 - Steel

Newall Security Mainspring No. 904 for 12s South Bend movements, Factory No. 55528, steel, new in envelope. See images for further details. I likely have several of these so the one you get may differ slightly from the images. 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.