FightLite Industries, SCR, Pistol Lower, 7075-T6 Forging, Polymer Grip.
Includes SCR Bolt Carrier (bolt not included), Carrier Strut & Strut Axis Pin.
To install your AR15 upper- you simply use the included bolt carrier, add your bolt of any caliber (5.56, 223, 300 BO, 6.5 Grendal, 6.8, etc), attach the included carrier strut and axis pin, and you are ready to go.
Article on the Fightlite SCR