Hamilton Factory Dynavar Mainspring for 20/0 & 21/0s Hamilton No. 717530- Alloy

Hamilton Factory Dynavar Mainspring for 20/0s & 21/0s Movements, Catalog No. 717571, alloy, new in envelope. Made for Grades 995, 995A, 997 & 721 and perhaps others. See image for precise characteristics. I 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.