Hamilton Factory Mainspring for 20/0-21/0s 17j Hamilton No. 718530

Hamilton Factory Mainspring for 20/0s & 21/0s 17 Jewel Movements, #718530, new in envelope. See image for precise characteristics. 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.