Hamilton Factory Dynavar Mainspring for 21/0s Hamilton Grades 750, 751, 761, 780 No. 46431 - Alloy

Hamilton Factory Dynavar Mainspring for 21/0s Movements, Grades 750, 751, 761, 780, Factory No. 46431 / 717570, alloy, 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.