this tactical looking black alloy scope mounted anticant bubble level accessory adapter fits to a 1" (25mm) with included spacer or 30mm tube of a scope, or any other 25 or 30mm diameter part of a gun so that a torch, laser, spotlight and other accessories can be fitted. Picatinny / weaver rail is 45mm long and 20.7mm wide. I have 222 Loctite listed and its recommended to use on the screws.