Swartchild Black Shield Clock Mainspring 5 x .30 mm x 25½" Ref 50-30 B 65

Swartchild & Co Black Shield Clock Mainspring, OPEN LOOP End, Ref. 50 - 30 B 65, from the 1950's, steel, made in France. See images for precise mainspring characteristics. 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