Swartchild Black Shield Clock Mainspring 3.5 x .205 mm x 23½" - Steel

Swartchild Black Shield Clock Mainspring, Tongue End, 26 x 3½ x 23½, from the 1940's or before. I 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