Don't. I bought a pair and when they stated sliding on the rail I tighten them when they started sliding again I tightened them again hearing a crack with each ring. The scope fell off in my hand. After looking at them I found there is only about an 1/8th square inch of material holding them . If the cross screw was put in lower there would be 1/8 inch bar of material all the way across the ring above the cross screw.