Precision Reflex PRi Fixed Rail Mounted Rear Sight w/ Thumb Wheel Black. Rail connects to rifle receiver with 3 cross bolts and the front of the rail connects to the 15in forearm. Rail is 20.5in in length with an add elevation of .450in. This top rail leaves room for a rear sight to be added to the receiver. The Rail comes with all hardware required to install top rail onto forearm. 8.5in rail will need to be removed. Specifications for Precision Reflex Pri Fixed Rail Mounted Rear Sights: Manufacturer: Precision Reflex Color: Black Condition: New Sight Mounting Orientation: Top Mounted Sight Position: Rear Gun Model: AR-15 Gun Make: AR Platform Front Sight Color: No Front Sight Rear Sight Color: Black Deployable: No Fabric/Material: T6 6061 Aluminum/ Cast Steel Front Blade Height: 1.4 in Gun Type: Rifle Included Accessories: Standard Weather Resistance: Yes Attachment Type: Single Cross Bolt Package Contents: Precision Reflex Pri Fixed Rail Mounted Rear Sights What firearm models does the manufacturer say Precision Reflex Pri Fixed Rail Mounted Rear Sights is compatible with? The manufacturer says that Precision Reflex Pri Fixed Rail Mounted Rear Sights is compatible with AR-15Precision Reflex 05-0129: PRi Fixed Rail Mounted Rear Sight w/ Thumb Wheel Black