Alloy Mainspring for AS caliber 1720

Unmarked Maker Swiss Mainspring for AS caliber 1720 movements plus perhaps similar ébauche watches, GR Ref. 5184, 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.