AR15 complete lower build kit contains every you need to finish out your stripped lower receiver 

-Lower Parts Kit

-Buffer Tube Kit 

Complete Lower Parts Kit Includes:

• Hammer
• Trigger
• Disconnect
• Bolt Catch
• Bolt Catch Detent
• Selector
• Selector Detent
• Magazine Catch Assembly
• Fire Control Group Pins (2)
• Takedown Pin
• Pivot Pin
• Takedown Pin/Pivot Pin Detents (2)
• Buffer Retainer Pin
• Complete Spring Kit
• Trigger Guard Assembly
• A2 Pistol Grip Assembly

Buffer Tube Kit Includes:

• Buffer Tube, 7075-T6, Hard Coat Anodized
• Carbine Buffer
• Castle Nut, Phosphate
• Endplate, Phosphate 
• Buffer Spring, Standard Music Wire