Swartchild Black Shield Clock OPEN LOOP Mainspring 3.50 x .32mm x 32½"

Swartchild & Co Clock Mainspring, OPEN LOOP End, Dennison 9/64 x .012 x 32½, from the 1950's, steel, new in envelope. See images for further details. The stain on the envelope is leftover tape sticky-goo. 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