Swartchild Black Shield SUPER Mainspring for ETA 900, Gruen 421, 422, 423 - Alloy

Swartchild Black Shield SUPER Mainspring for ETA caliber 900 and Gruen caliber 421, 422, 423 movements plus perhaps similar ébauche watches, white alloy, new in envelope. See images for precise mainspring specifications.  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.