Swartchild Black Shield Mainspring for Seth Thomas 18s No. 729 - Steel

Swartchild Black Shield Mainspring #4398 for Seth Thomas 18s movements, Factory No. 729, steel, new in dirty envelope. See images for further details. I likely have several of these so the one you get may differ slightly from the images. I specialize is hard to find watch parts and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.