Alloy Mainspring for Font (FHF) caliber 57, 57-21

Unmarked Maker Swiss Mainspring for Font caliber 57, 57-21 round 6¾ ligne movements plus perhaps similar ébauche watches, white alloy, new in tiny envelope. See images for precise mainspring specifications.  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.