Electro Mainspring for 3L Longines caliber 4.21 - Steel

JAR Electro steel mainspring "No. 1" for 3 ligne Longines caliber 4.21 and perhaps other wrist watches, new in envelope. See images for precise mainspring specifications. I've never seen this maker before and I'll speculate that they may have never made another mainspring past "No.2" (which I also have). 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.