Marco Mainspring #710 for 16s N.Y. Standard Factory No. 1731 - Steel

Marco Mainspring #710 for 16s N.Y. Standard, Factory No. 1731, steel, new in envelope. Typically found in the Excelsior marked movements but fit others as well. 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.