Longines Factory Mainspring for caliber 4LL - Steel

Longines Factory Mainspring caliber 4.LL plus perhaps similar ébauche watches, steel, new in sealed envelope. The wonderful thing about factory mainsprings is they always fit! I know it says unbreakable but I suspect it is still a steel mainspring. 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.