Swartchild Black Shield Mainspring for NY Standard 10s No. 7080 - Steel

Swartchild & Co Black Shield Mainspring No.441002 for N.Y. Standard 10s movements, factory No. 7080, tongue end, steel, new in envelope. Swartchild Mainspring Catalog (which I sell) lists this as a Dennison 6 x 6½. See images for further details. I specialize in hard to find watch parts and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.