I believe the Receiver, hammer, trigger, sear, grip frame, trigger housing, barrel, and cocking handle. Maybe the flash suppressor as well. Per their website: PTR maintains a minimum of 7 U.S. parts in all products. Many of the parts in your PTR are manufactured by PTR, if not all. However the US parts count in PTR’s products can vary. Most H&K and G3 parts are interchangeable with PTR’s design and because of this we recommend consulting our staff prior to switching any parts on your rifle.