KBK Mainspring #3817 for Elgin 12s No. 1712 - Steel

KBK Genuine Factory Mainspring #3817 for Elgin 12s movements, Factory No. 1712, steel, new in envelope. See image for precise specifications. Not very familiar with the supply house (would love to find them in a catalog), but it says Genuine Factory and indeed the spring is marked E.N.Co on the end. 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.