USR Mainspring for Hampden 16s No. 3696 - Steel

USR Mainspring for Hamilton 16s 3/4 Plate Pocket Watches (Wm McKinley), Factory No. 3693, steel, new in envelope. Because the envelope either open or perhaps torn, they're usually pretty dusty so they'll need a good cleaning before, but all mainsprings should be cleaned before use anyhow. USR is short for Ulysse Sandoz-Robert of La Chaux-de-Fonds, Switzerland. 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.