Illinois Factory Mainspring No. 47313 for 16s 21j & 23j movements - Steel

Illinois Factory Mainspring, Factory No. 47313 for 16s 21j & 23j movements, steel, new in envelope. One of the beautiful thing about factory mainsprings is that they pretty much always fit. See images for further details. 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 and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.