Swartchild Black Shield Mainspring 4396E for Crown (NY Standard) 3/0s No. 1323 - Steel

Swartchild Black Shield Mainspring 4396E for 3/0s Crown, made by New York Standard, Factory No. 1323, steel, new in envelope. See images for further details. Not an easy mainspring to find. I specialize is 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.