Hamilton Dynavar 10s Mainspring for 917, 921, 923 & 945 No. 20433 - Alloy

Hamilton Dynavar Factory Mainspring for 10s Movements, more specifically the models 917, 921, 923 and 945, Factory No. 20433, alloy, 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 is hard to find watch parts and all watch parts are unconditionally guaranteed. Images do an adequate job of representing the item.