Evolution Gun Works Universal Trijicon RMR Sight Mount .670in Radius 1.780in Aluminum Matte Black Hardcoat. 780"Overall Width:1.1"Overall Height: .335"Radius: .468"Mounting Hardware:(2) 6-32 Flat Head Screws (1) 6-32 Set ScrewRed Dot Fitment:Trijicon RMR Holosun HS507CThis mount has a bottom radius of .468". There should be a slight gap at the top of the radius between the receiver and the mount when mounted. The two spreads on this mount measure .500"-.505" and .8625".This should fit barrel/receiver diameters from .936"-1.350". Specifications for Evolution Gun Works Universal Trijicon RMR Sight Mount 1.780 in Aluminum: Manufacturer: Evolution Gun Works Color: Black Finish: Matte Gun Model: Universal Fabric/Material: Aluminum Red Dot Sights-Footprint: RMR Optic Cut: Not Applicable Length: 1.78 in Package Contents: Evolution Gun Works Universal Trijicon RMR Sight Mount 1.780 in Aluminum Evolution Gun Works 49525: Universal Trijicon RMR Mount .670 in Radius 1.780 in Aluminum Matte Black Hardcoat