Swartchild Black Shield Clock Mainspring 5.6 x .21 mm x 27" DB&H end - Steel

Swartchild Black Shield Clock Mainspring, DB&H End, Dennison 48 x 3 x 27", for unspecified clock movements likely from the 1940's or before. I likely have several of these so the exact packaging may be different. I specialize is hard to find watch & clock parts and all parts are unconditionally guaranteed. Images do a pretty good job of representing the item