NuREZISTA Mainspring #640 for Hamilton 6/0s Factory No. 1721 - Steel

NuREZISTA Mainspring #640 for Hamilton 6/0s Movements, Factory No. 1721, steel, new in envelope. See images for specifications and further details. 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.