C&E Marshall Marshalloy Mainspring 3684M for Vulcain 640 to 643 & Tavannes 566, 577 - Alloy

C&E Marshall Marshalloy Mainspring 3684M for Vulcain 640, 642, 643, Cyma / Tavannes 566, 577, 3817 caliber movements, alloy, new in envelope. See images for precise mainspring specifications and 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 an adequate job of representing the item.