HR Mainspring SA731 for Waltham 0s Factory No. 2228 - Alloy

HR Mainspring SA731 for 0s Waltham, Factory No. 2228, alloy, new in envelope. This is also known to fit some 3/0s movements as well. See image 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 unconditionally guaranteed. Images do an adequate job of representing the item.