Kilb-Beck Mainspring #3017 for Hampden 8/0s No. 15696 - Steel

Kilk-Beck Company Mainspring #3017 for 8/0s Hampden movements, including the Mary Jane & Josephine, Factory No. 15696, steel, new in envelope. See image for precise specifications. Not very familiar with the Kilb-Beck supply house and would love to find them in a catalog somewhere. 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.