The RL556v3 features Polymer80 s proprietary polymer composite, a solid core design, flared magwell, and beefier mil-spec buffer tube housing. The pistol grip area features a unique threadless design specific to Polymer80 rifle lowers. The kit includes: 80% Polymer AR15 Lower Receiver (Mil-spec) Polymer Jig Trigger Hole Drill Guide Drill Bits and End Mill