Swartchild Black Shield Mainspring #4395¾A for 16s N.Y. Standard 3196 - Steel

Swartchild & Co. Black Shield Mainspring #4395¾A for 16s N.Y. Standard "New Model" movements, Factory No. 3196 (or 1731), steel, T-end, new in envelope. See images for further details. Probably fits other American watches as well. I likely have several of these so the on 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 barely adequate job of representing the item.