These are original magazine springs removed from Act-Mag brand 15 round .40/10mm staggered magazines.  These are the magazines sold by / included with Rock Island Armory A2 HC .40 S&W and 10mm pistols.  They were removed from magazines that we converted to 9mm and the springs were never actually used - they were installed at the factory and then we removed them.

These would be good for replacing tired Act-Mag springs but I would not recommend them in the longer Mec-Gar magazines.