Alloy Mainspring for Excelsior Park caliber 1, 11

Unmarked Maker Swiss Mainspring for Excelsior Park caliber 1, 11 movements plus perhaps similar ébauche watches, GR Ref. 4519-1, 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.