Every DNZ scope mount is precision machined in North Carolina from top grade, solid billet aluminum. Ultralight with maximum shock absorption, there are no movable parts between rifle and scope. simply put, DNZ machines some of the finest, most accurate scope mounts in the world. Ruger American (centerfire): Mount fits both left and right hand firearms. Base screws are 6-48 X 1/4? long. Ring screws are 6-40 X 5/8? long. Both screws use a 7/64? Allen wrench. Short action ? Outside to outside of rings is 3.97?. Standard rings are .63? wide and have 2 ring screws per ring. 4 Hole to hole spacing dimensions are .86?, 3.01?, .86?. Height of mounts from top of receiver to centerline of scope tube is - low .92?, medium 1.05?, and high 1.17?. Long action ? Outside to outside of rings is 4.49?. Standard rings are .63? wide and have 2 ring screws per ring. 4 Hole to hole spacing dimensions are .86?, 3.54?, .86?. Height of mounts from top of receiver to centerline of scope tube is - low .92?, medium 1.05?, and high 1.17?.