Rolex Factory Mainspring for caliber 4U & U7 movements - Alloy

Rolex factory mainspring for caliber 4U and U7 movements and quite likely others, alloy, new in envelope. My books show this as a Dennison 6 x 15 x 6½ (metric 1.50 x .06) with a tongue end. I specialize is hard to find watch parts so I usually have whatever you might need and all watch parts are unconditionally guaranteed. Images do a pretty good job of representing the item.