Rainier Arms RUC DI 5.56 NATO Complete Upper 16in Black Medium. Bringing the highest quality parts to the market while offering the best value as well. This complete upper utilizes a direct impingement operating system on their new and improved Rainier Arms Select barrel. Pairing up with their Urban Combat Rail to provide shooters with a rock solid handguard that can take any abuse. The complete upper is finished off with their Rainier Industries Avalanche ANC charging handle and their Rainier Arms FHV2 Flash Hider. Specifications for Rainier Arms RUC DI 5.56 NATO Complete Upper: Manufacturer: Rainier Arms Caliber: 5.56x45mm NATO Barrel Length: 16 in Gas System Length: Mid Length Threads per Inch: 1/2x28 Color: Black Gun Model: AR-15 Fabric/Material: 416R Stainless Steel Nitrided Gas Block Journal Size-Diameter: .750 in Gun Type: Rifle Gun Make: AR Platform Magazine Included: No Package Contents: Rainier Arms RUC DI 5.56 NATO Complete Upper What firearm models does the manufacturer say Rainier Arms RUC DI 5.56 NATO Complete Upper is compatible with? The manufacturer suggests that Rainier Arms RUC DI 5.56 NATO Complete Upper is compatible with AR-15Rainier Arms RA-RUC-DI-16M-CU: RUC DI 5.56 NATO Complete Upper 16in Black Medium