Hunt Masters signature series two piece scope mounts : Fits long and short actions, some super short actions - left and right hand guns Custom made to fit each type of firearm and align perfectly with your rifle's receiver Each ring and base is machined from a solid block of top-grade billet aluminum Internal ring and base design allows for extra eye relief adjustment Eliminates or reduces scope damage from tightening rings Approximately 1/3 the weight of steel Eliminates the need for windage screws that can work loose and cause problems No moving parts between the firearm and the scope Up to four times the threads of other mounts for absolute strength and security Absorbs shock and withstands temperature extremes better than steel mounts at a fraction of the weight Made in the USA Browning X Bolt (fits all action lengths): Base screws are 6-48 X 1/4? long. Ring screws are 6-40 X 5/8? long. Both use a 7/64 Allen wrench. Hole spacing dimensions on front mount and back mount are .70?. Both mounts are not the same part. Back mount is taller than front mount because receiver is lower on back end. Standard rings are .63? wide and Tactical rings are .80? wide. Standard rings have 2 screws per ring and Tactical rings have 4 screws per ring. Height of mounts from top of receiver to centerline of scope tube is - low .94?, medium 1.06?, and High 1.19?.