Spikes Tactical M4 Flat Top Upper. Built with the same high quality that is used on factory builds these AR15 Upper Receivers by Spikes Tactical are constructed from 7075 T6 aluminum and feature a forward assist as well as an ejection port door making installation easy. Make sure your rifle is operating at peak efficiency install the Spikes Tactical M4 Aluminum Flat Upper. Specifications for Spikes Tactical M4 Flat Top Upper: Manufacturer: Spikes Tactical Color: Black Finish: Anodized Fabric/Material: 7075 T6 Construction Caliber: 5.56x45mm NATO Gun Model: M4 Condition: New Country of Origin: USA Features of Spikes Tactical M4 Picatinny Upper: Machined from a Mil-Spec 7075 T6 forging Type III Hardcoat Anodized finish Ejection port door cover and forward assist come pre-installed Chambered in 5.56x45mm NATO Package Contents: Spikes Tactical M4 Flat Top Upper What firearm models does the manufacturer say Spikes Tactical M4 Flat Top Upper is compatible with? The manufacturer says that Spikes Tactical M4 Flat Top Upper is compatible with M4Spikes Tactical SFT50M4 Upper Receiver - Forged M4 Flat Top Multi Cal