Hamilton Factory Mainspring for 21/0s Hamilton Grades 750 & 751 No. 7421 - Steel

Hamilton Factory Mainspring for 21/0s Movements, Grades 750 & 751, Catalog No. 7421, steel, new in envelope. See image for precise characteristics. 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 so I usually have whatever you might need and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.