Lower Receiver A2 Build Kits - QuickSet Takedown & Pivot PinsLower Receiver Lower Receiver Build Kits QuickSet Takedown & Pivot Pins The Lower Receiver Build Kit with the NexGenAR QuickSet Takedown and Pivot Pins is a great quality kit that includes all of the necessary parts needed to build out your lower receiver. Features: Size: Mil Spec. Compatibility: Should fit most Mil Spec. AR15 rifle configurations, but refer to your manufacture for more specific compatibility information Common Calibers: . 223, 5. 56,