Swartchild Black Shield Mainspring for Hamilton 12s #1228 - Steel

Swartchild & Co Black Shield Mainspring No.4372D for Hamilton 12s movements, Factory No. 1228, steel, new in envelope. Swartchild Mainspring Catalog (which I sell) lists this as a Dennison 8 x 5½. See image for further details. As was surprisingly common for Swartchild, the envelope may be marked incorrectly as a 1224 which never existed in Hamilton's catalogs. 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.