Marathon Mainspring #221 for Elgin 10/0s, & 16/0s & 18/0s No. 1957 - Steel

Marathon steel mainspring No. 221 for Elgin 10/0s, 16/0s & 18/0s movements, Factory No. 1957, new in envelope. See images for precise mainspring specifications. 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.