Feature a Adjustable Length Allows for Comfortable Eye Relief, Improving Shooting Accuracy a Additional 0.3, 0.65, and 1.65 inch for Forward Extension to Customize Eye Relief a 38mm/ 1.5in Bottom to Ring Center, Extremely Accurate and Stable w/ Full CNC Machined a 21mm Picatinny Mount with Two Crossing Bolts & Anti-Retreat Bar for A Secure Attachment Specification Ring Diameter: 30 mm Overall Length: 139 mm / 5.47 in Overall Height: 62.0 mm / 2.44 in Ring Width: 45.5 mm / 1.79 in Central Height: 38.0 mm / 1.5 in, Bottom to Center Gap Length: 73 mm / 2.87 in Material: 6061-T6 Aluminum Alloy Weight: 154 g / 5.43 oz Mount: 1913 Picatinny Finish: Black Screws per ring: 4 (M4 x 9mm) Mount Material: 6061-T6 Aluminum Alloy Items in the Package: Hex Key, T15 Torx Wrench and T20 Torx Wrench, etc. Video