DNZ's Game Reaper is precision machined from a solid block of top-grade billet aluminum, and is custom made to fit each type of firearm and align perfectly with your rifle receiver with no moving parts between the firearm and the scope. The Game Reaper absorbs shock and withstands temperature extremes better than steel mounts. Base screws are 8-40 X 1/4 long and 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.