1. Top flat picatinny rails, other three sides key hole cutout 2 .Overall Length: 180mm (7 inch) 3. Weight (net): 390g 4. Inside Dia 35mm (1.4 inch) 5 .Lower rail style with CNC procedure 6 .One piece style more accurate 7 Upper rail is extended over the barrel nut for a 'no-gap' monolithic look 8 Light weight in precision 9 Easy and quick installation 10. High quality aluminum alloy in durable mil-spec style black matte finish 11.With tools, 2 pcs 3" detachable picatinny rails 12.Shock proof can be used on real fire caliber