Advance Superior Mainspring #766 for Illinois 16s 60hr MB No. 1759 / 47309 - Steel

Advance Superior Mainspring 766 for Illinois 16s 60hr Motor Barrel movements, Factory No. 1759 / 47309, new in very frail envelope. See images for precise mainspring specifications details. These are 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.