HR Mainspring A509 for 12s NY Standard Factory No. 4144 - Steel

HR Mainspring A509 for NY Standard 12s Movements, #4144, T-end, steel, new in envelope. See image for precise characteristics. 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.