Tru-Time Mainspring - Elgin 5550 for 15/0s movements - Steel

Tru-Time Mainspring for Elgin 15/0s movements, Factory No. 5550, steel, new in possibly frail envelope. 15/0s are usually grades 536, 537, 538, 557, 558, 559, 623, 624 & 626.  See images for precise mainspring specifications. 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.