BOREL Mainspring or 21/0s Hamilton No. 7421 / 46432 / 717571 - Alloy

BOREL Mainspring for 21/0s Hamilton Grade 750, 751, 756 & 757 Movements, Factory No. 7421 / 46432 / 717571, alloy, tongue end, new in envelope. See images for precise mainspring specifications. 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.