Gruen Factory Mainspring for caliber 275, 280, 285 & 540 movements - steel

Gruen Factory mainspring for caliber 275, 280, 285 & 540 movements, and quite likely others, steel, new in 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, even the ones that say unbreakable as they're still just steel mainsprings. 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.