Gruen Factory Mainspring for caliber 290, 291 - Steel

Gruen Factory mainspring for caliber 290, 291 and quite likely others, steel, new in open envelope. I likely have several of the so the one you get may differ slightly from the images but they are all the same mainspring. Gruen also had the annoying practice of marking many their Steel mainsprings as unbreakable, which everyone else attributes to alloy, which these are not..  I specialize in hard to find watch parts so I usually have whatever you might need and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.