Newall Security Mainspring #766 for Illinois 16s 60hr MB No. 1759 / 47310 - Steel

Newall Security Mainspring No. 766 for Illinois 16s 60hr Motor Barrel movements, Factory No. 1759 (new No. 47310), new in (distressed) envelope. See image for further details. I likely have several of these so he 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.