AR 15 is considered one of the best rifles to buy for customization depends upon the purpose you are planning to have it you can modify it to any extent. Below listed are the lower parts of an AR 15
· AR-15 Lower Receiver (stripped or the 80% lower receiver)
· Buttstock / Pistol brace
· Buffer buffer spring and buffer tube
· Trigger group- it entails the trigger, hammer, and dis-connector.