Swartchild Black Shield Mainspring #11781 for Howard 12s No. 553 - Steel

Swartchild & Co Black Shield Mainspring No.11781 for Howard 12s movements, Factory No. 553, steel, new in envelope. Swartchild Mainspring Catalog (which I sell) lists this as a Dennison 10 x 7. 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.