Steel Mainspring for Trenton 3/0s Grade 90 Movements

Generic Steel Mainspring for Trenton 3/0s, T-end, 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 also have no reference for whether a P/N was assigned to this grade's mainspring but I haven't found it yet. I did measure them at a Dennison 6 x 6. 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.