Advance Mainspring No. 463 for Elgin 15/0s Factory No. 5550 - Steel

Advance Mainspring No. 463 for Elgin 15/0s movements Factory No. 5550, steel, new in envelope. 15/0s are usually grades 536, 537, 538, 557, 558, 559, 623, 624 & 626. See images for precise characteristics. I specialize in hard to find watch parts and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.