H. & W. Perrin Co. Mainspring for FEF calibers 40 to 49 - Steel

H. & W. Perrin Co Mainspring for FEF caliber 40 to 49 movements and likely others as well,steel, new in envelope. See images for precise mainspring specifications. H. & W. Perrin is the largest supplier of horological materials in Canada. Images do an adequate job of representing the item.