Hamilton 12s Mainspring #1228 Made by Waltham - Steel

Hamilton Mainspring for 12s, Factory No. 1228, marked M.B. (which is supposed to mean Double Brace) made by Waltham, steel, new in envelope. This is not the first time I've run across a mainspring that Waltham made for a competing brand. Still it's a nice quality mainspring - and cheap too! I specialize in hard to find watch parts and all watch parts are unconditionally guaranteed. Images do an adequate but perhaps incomplete job of representing the item.