Hamilton Factory Mainspring for 20/0s & 21/0 Factory No. 718531 / 2921 - Steel

Hamilton Factory Mainspring for 20/0s & 21/0 Movements, Factory No. 718531, steel, new in envelope. See images for precise mainspring specifications. I may have several of these so the one you get may vary 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.