Swartchild Black Shield Mainspring #48503, 2.00 x .11 mm x 12½" - Steel

Swartchild Black Shield Mainspring No. 48503, Dennison 11 x 10 x 12½", for unspecified Swiss movements likely from the 1940's or before, regular Tongue end, steel, new in envelope. These springs were packaged with clock mainsprings but since they don't specify what they're for I suppose they can be used wherever they'll fit. 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