UP100 Tactical Integral Offset 30mm Ring Mount Rifle Scope Weaver Picatinny See-through 20mm Rail Base Mount for Hunting Aluminum Alloy with Anodized Black Matte Finish Fits 20mm Picatinny/Weaver Rails Hex Screws Guarantee Easy Installationand; 38mm Bi-directional Offset Provides Extended and Comfortable Eye Relief Ring Distance from Outer Edge to Outer Edge 75mm; Ring Distance from Inner Edge to Outer Edge 39mm Ring Diameter: 30mm; Rail: 20mm