HR Mainspring SA653 for Seth Thomas 18s Factory No. 729 - Alloy

HR Mainspring SA653 for Seth Thomas 18s movements, Factory No. 729, alloy, new in envelope. See images for precise mainspring specifications. I likely have several of thee 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.