The Present Arms AR-15 Lower Repair Block is machined from synthetic non-marring polymer providing added support inside and out of the lower receiver. Securely held when pinned with the takedown and pivot pins of the receiver. The receiver can be mounted in both upright and inverted position for full access when assembling and disassembling. To be used with the Present Arms Patented Receiver Alignment Block. Ensuring correct 12-6 alignment of the receiver extension tube. Ensure correct stock alignment. The perfect platform and mount for the armorer. Mfg: Present Arms Inc