The Patented lower receiver 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 our Patented Receiver Alignment Block. Ensuring correct 12-6 alignment of the receiver extension tube.