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; Base screws are 6-48 x 1/4" long; Ring screws are 6-40 x 5/8" long; Both screws use 7/64 Allen wrench; Outside to outside of rings is 4.60"; Standard rings have 2 screws per ring and rings are .63" wide; Fits both left and right hand firearms; Made in the USA