Volquartsen Firearms TL Rear Sight for Mark II III IV Black. No fitting required uses factory dovetail locks in place with two set screws. Made of steel. Rear sight notch width .110". Fits Ruger MKII MKIII and MK IV to replace factory rear adjustable sight. This sight is only compatible with uppers with 0.875in bull barrels This replaces the rear sight on factory Ruger uppers. Specifications for Volquartsen Firearms TL Rear Sight for Mark II III IV: Manufacturer: Volquartsen Firearms Gun Make: Ruger Gun Model: Ruger Mark IV Ruger Mark III Ruger Mark II Color: Black Fabric/Material: Steel Gun Type: Rifle Attachment Type: Screw Package Contents: Volquartsen Firearms TL Rear Sight for Mark II III IV What firearm models does the manufacturer say Volquartsen Firearms TL Rear Sight for Mark II III IV is compatible with? The manufacturer suggests that Volquartsen Firearms TL Rear Sight for Mark II III IV is compatible with Ruger Mark II Ruger Mark III Ruger Mark IVVolquartsen Firearms VC2TL: TL Rear Sight for Mark II III IV Black