Adds 5 rounds to the S15 magazine; Unique easy access floor plate design to service or clean the magazine body without the need to remove the magazine extension from the magazine body; Index cuts on the extension body to increase grip when coming out of a magazine pouch; Machined from billet 6061 aluminum; Type 2 anodized; Comes with a 12 coil plus power spring; Fits Shield Arms S15 magazine only; Fits most aftermarket flared mag wells; Proudly made in the USA