NuREZISTA Mainspring #537B for 21/0s Elgin Factory No. 5327 - Alloy

NuREZISTA Mainspring #537B for 21/0s Elgin Movements, Factory No. 5327, alloy, D.B. end, new in envelope. See image for precise mainspring specifications. 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 guaranteed. Images do a satisfactory job of representing the item.