Kilb-Beck Mainspring #3918 for Hamilton 6/0s No. 2621 - Steel

Kilk-Beck Company Mainspring #3918 for 6/0s Hamilton movements, Factory No. 2621, steel, new in envelope. See images for precise specifications. Not very familiar with the Kilb-Beck supply house and would love to find them in a catalog somewhere - they are pretty nice mainsprings. 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.