Precision machined from a solid block of top-grade billet 6061T6 aluminum; Custom made to fit each type of firearm and align perfectly with your rifle's receiver; No moving parts between the firearm and the scope; 67% lighter than comparable one-piece mounts with four times the threads and precision socket-head cap screws for absolute strength and security; Absorbs shock and withstands temperature extremes better than steel mounts at a fraction of the weight; Mount fits both left and right hand firearms; Base screws are 8-40 x 1/4" long; Ring screws are 6-40 x 5/8" long; Base screws use a 9/64" Allen wrench and ring screws use a 7/64" Allen wrench; Outside to outside of rings is 3.92"; Standard rings are .63" wide and have 2 ring screws per ring; Made in the USA