Croton Duranium Alloy Mainspring for FEF caliber 250

Croton Nivada Grenchen Duranium Mainspring for 8¾ ligne Fleurier (FEF) caliber 250 movement plus perhaps similar ébauche watches as well, alloy, new in envelope. See images for further details. I likely have several of these so the one you get may differ slightly from the images. 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.