Swartchild Black Shield Mainspring No. 4382 for Illinois 6s Factory No. 47353 - Steel

Swartchild & Co Black Shield Mainspring No.4382 for Illinois 6s 1st Model movements, Factory No. 47353 or No. 171 depending how old of a catalog you use, steel, new in envelope. Swartchild Mainspring Catalog (which I sell) lists this as a Dennison 9 x 6½. 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.