Comsco Mainspring #11111 for Hamilton 10s Factory No. 6021 - Steel

Comsco Mainspring #11111 for Hamilton 10s Movements, Factory No. 6021, steel, new in frail  envelope. Distributed by Burton M. Reid and Sons. See image for precise mainspring specifications and further details. Not a particularly common mainspring. 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.