From Ruger®, a stripped lower receiver for AR-556. The 7075-T6 aluminum lower receiver is finished in a black finish, ready for your next AR build. For 5.56 mm NATO and .223 Remington. 

I have 5 available with a mix of serial numbers, and three sets of two receivers each that are sequential serial numbers. Sequential receivers will only be sold as pairs, they are $218 before tax and background check or shipping.