The Shield Arms SA-15 Folding Billet AR-15 Stripped Lower Receiver is the perfect starting point for your next AR-15 build. FeaturesMachined from 7075-T6 aircraft grade billet aluminumMil-Spec dimensionsAccepts standard AR-15 magazinesMatte black hard-coat anodized per Mil 8625 Type 3 Class 2Precision machined magazine well with beveled feed lip for easy mag changesCaliber marking of "MULTI"Compatible with most standard AR-15 components and most aftermarket partsUpper tension screw behind grip screw (threaded hole with hardware included) to adjust any "slop" out of vertical fit between upper and lowerThreaded bolt catch pin (threaded hole and hardware included)