NuVigor Mainspring #521 for South Bend 16s No. No. 37528 - Steel

NuVigor Mainspring #521 for South Bend 16s movements, Factory No. 37528, T-end, steel, new in envelope. See images for further details and precise mainspring specifications. These are super hard to find so grab one while you can. I may have several of these so the one you get may differ slightly from the images. I specialize is hard to find watch parts and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item