Kilb-Beck Mainspring #3914 for Hamilton 0s No. 1536 - Steel

Kilk-Beck Company Mainspring #3914 for 0s Hamilton movements, Factory No. 1536, 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. 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.