Matador Arms MAT-9K AR-9 9mm 5in Roller Delayed Upper Reciever 4150 Lightweight Nitrided Barrel 1-10 Twist 1/2x28 Threads Anodized Gray. The 9mm upper is machined for maximum weight reduction slim profile and compatibility with bolt catches and lower receivers. The upper is also built with a tapered multi-material 4-piece trunnion system to maintain mechanical accuracy and durability. The MAT-9 9mm AR upper is compatible with AR-9 Lower receivers in any double-stack magazine configuration: Glock Sig Sauer Colt Stick Magazines HK MP5 CZ Evo Scorpion. With an AR-15 Lower Receiver it requires Matador Arms Mag-X magazine conversion kit or equivalent type product such as Endomag. The Roller Delayed system designed for our MAT-9K upper reduces recoil lightens the upper and increases reliability. The lack of a need for buffer tubes increases agility and portability in compact spaces. The flexibility of the non-reciprocating and reversible charging handle makes the MAT-9 the perfect platform for any shooter. Specifications for Matador Arms MAT-9K AR-9 9mm 5in Roller Delayed Upper Receiver: Manufacturer: Matador Arms Caliber: 9mm Luger Barrel Length: 5 in Barrel Profile: Tactical Lightweight Barrel Twist Rate: 1-10 Threads per Inch: 1/2x28 Muzzle Device: Thread Protector Finish: Anodized Fabric/Material: 6061-T6 Aluminum Handguard Length: 13 in Gun Rail: M-LOK Gun Make: AR Platform Gun Model: AR-9 Barrel Material: 4150 CMV Steel Features of Matador Arms MAT-9K AR-9 9mm 5in Roller Delayed Upper Receiver Non-reciprocating steel charging handle (ambidexterous) 4140 Nitrided steel bolt and action parts 6061-T6 anodized upper receiver 4150 Lightweight Nitrided Barrel 5in long 1:10 twist 1/2x28 threads NATO 1913 Spec top rail 1 MLOK slot (both sides bottom) Compatible with LRBHO (Last Round Bolt Hold Open) lower receiver Ready to run with a Suppressor right out of the box Roller Delayed operating system Package Contents: Matador Arms MAT-9K AR-9 9mm 5in Roller Delayed Upper Receiver What firearm models does the manufacturer say Matador Arms MAT-9K AR-9 9mm 5in Roller Delayed Upper Receiver is compatible with? The manufacturer says that Matador Arms MAT-9K AR-9 9mm 5in Roller Delayed Upper Receiver is compatible with AR-9Matador Arms MATK-U-GRYOP: MAT-9K AR-9 9mm 5in Roller Delayed Upper Reciever 4150 Lightweight Nitrided Barrel 1-10 Twist 1/2x28 Threads Gray