Full Size Aluminum Mainspring Housings custom machined out of 6082-T6 Aluminum. This is the same aluminum used in the racing bikes on the tour de france. We then have the aggressive checkered texture machined into them. A quick bead blast and off to the anodizer they go. They all get a Type III Hard Anodize which produces a coating that is denser and more abrasive resistant than your regular sulfuric anodizing. The Aluminum Mainspring Housing weighs in at only 17 grams which is 2.6 times less than the same MSH made out of steel. They come ready for your favorite gunsmith to install. So do you really want that Plastic MSH in your $900+ gun?