Swartchild Black Shield Mainspring for Hampden 16s No. 3696 - Steel

Swartchild & Co Black Shield Mainspring for Hampden 16s ¾ plate models, Factory No. 3696, steel, new in envelope. See images for further details.  This is a somewhat lighter strength mainspring that usual at .20 (Dennison 3½) so it's likely for higher jewel movements. 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.