In the AR15 platform, all are standard, except for the buffer tube, you have two types, Commercial and Mil-Spec, depending on which buffer tube you purchase, you need to purchase same type of stock, Commercial or Mil-Spec. On an AR10 platform, you have to be careful, no real set standard, better to purchase a builder's kit to match the Lower and Upper receiver to work together, everything else is pretty much the same. What is great about the AR's is you can customize to what you want, I will never purchase another one already built, I ended up changing all the components on my Bushmaster Carbon-15, just kept the Lower... My next build is an AR10 and plan to purchase the Aero Precision builder's kit, good luck on your build, the barrel and trigger is where I would not go cheap.