Star Mainspring for 0s U. S. Watch Co No. 327 - Steel

STAR Mainspring for 0s U. S. Watch Co early model Pocket Watches, Factory No. 327, steel, new in envelope. Mainspring could be suitable for other 0s watches as well. The 0s U.S. Watch specified a Dennison width of 4½ or 5 depending on your source. See images for precise mainspring specifications.  I specialize in hard to find watch parts and all watch parts are unconditionally guaranteed. Images do an adequate job of representing the item.