Steel Mainspring for N. Y. Standard 0s #6133

Generic Steel Mainspring for N. Y. Standard 0s, Factory No. 5133, new envelope. Usually I have some idea who made specific mainsprings but the envelopes don't show a maker, just the information you see here. I did measure them at a Dennison 6 x 7 so they are indeed as marked. 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.