Borel Mainspring for Elgin 16s Motor Barrel models No. 4931 - Alloy

Borel Mainspring for Elgin 16s Motor Barrel Models and perhaps others, Factory No. 4931, alloy, new in envelope. See images for precise mainspring specifications. You may notice that the specs for this mainspring are very, very similar to an 817.  I likely have several of these so the one you get may differ slightly from the images. I specialize in hard to find watch parts and all watch parts are guaranteed. Images do a pretty good job of representing the item.