Angstadt Arms complete upper receiver pistol assembly is ready to run out of the box with any 9mm AR-15 lower receiver. Featuring the same high quality parts that go into are UDP-9 pistol, this completed upper receiver is compatible with both GLOCK(R) and COLT(R) style 9mm magazines. Features: 7075-T6 billet aluminum slick side pistol caliber upper receiver with appropriately sized ejection port 10.5? 9mm lightweight profile barrel made from 4150 chrome-moly steel with a 1-10" twist rate. 1/2x28 TPI 10" ultra light skeletonized handguard with M-LOK(R) mounting interface on the 3, 6, & 9 O'clock positions The hand guard features 4 QD swivel mounting points and a top mil-spec 1913 lightening cut picatinny rail with skeletonized M-LOK(R) mounting sections Handguard ID: 1.375* The last 3/4" of the handguard is bored out to 1.405", allowing most aftermarket sound suppressors 1.39" in diameter and smaller to tuck inside of the handguard Black nitride 9mm AR-15 bolt carrier group. For use with a standard AR-15 hammer Compatible with both GLOCK(R) and COLT(R) style 9mm dedicated lower receivers. Angstadt Arms 9mm flash hider Mil-spec charging handle Caliber: 9mm NATO