Swartchild Black Shield Clock OPEN LOOP Mainspring 4.80 x .41mm x 54" - MS-253

Swartchild & Co Clock Mainspring, OPEN LOOP End, Dennison 3/16 x .016 x 54, P/N MS-253 (80-504) from the 1950's or later, steel, new in envelope. See images for further details. My guess is this is for an 8-Day clock, based on the length of the mainspring, although I don't know which one. I'll also point out that these need some serious cleaning before use. I specialize in hard to find watch & clock parts and all parts are unconditionally guaranteed. Images do a pretty good job of representing the item