Heavy duty Picatinny rings are precision machined from solid aluminum billet as matched pairs to aid in obtaining the best possible alignment. Each pair is clamped together and the center holes bored to 30mm to tolerances of +/-.0014", then engraved with matching serial number. In addition, the lower halves are marked to prevent separation from their matched ring caps. All edges are beveled or radiused, including both sides of the steel ring nut, to minimize potential for snagging on other gear. Surfaces are blasted to ensure an even, matte finish, then hard anodized with a durable black finish for added strength and wear resistance. Crossbolt and nut are machined from chrome-moly steel, hea Mfg: Egw SPECS: Rings X"X Body: Aluminum, hardcoat anodized, matte black. Crossbolts/Nuts/Cap Screws X"X Chrome-moly steel, blued. Height from top of base to inside bottom of ring: .400" (10.1mm). Fits scopes with 30mm O.D. tubes. Mounts to MIL-STD 1913 Picatinny bases. Inserts X"X Machined polymer, black.