The AR lower receiver is the basic serialized piece of the AR platform. Part of the AR's appeal is the ability to completely customize and build a firearm from the ground up, using whatever parts you want to use from surplus all the way to match grade. Just FYI, the term "AR" originally stood for Armalite, the first manufacturer of the AR platform, please feel free to correct anyone who mistakenly calls it an "assault rifle". Most frames are aluminum, a few are magnesium for high strength and low weight. You might hear of forged vs milled and notice a price difference. Forged lowers are cast into rough blanks and then finish machined into complete receivers, while milled are machined down from a solid block of aluminum, which some argue makes them more durable. We carry the top brands like Anderson, DPMS, Spike's, Black Rain, Noveske, Mag Tactical Patriot Ordnance, S&W, and more.