"I bought this to bring my red dot up to Cowitness my BUIS. I get them home and quickly realize that these must SLIDE onto the rail instead of clamping on. After putting the screws back in and tightening them down I realize that they wiggle. Not just a little, but A LOT. I mounted these, or tried to mount these, on a Spikes Tactical ST-22 Flattop Upper and a Bushmaster Flattop Upper. Both times they wiggled and left scratches. I knew they would be cheap, but I thought they would at least have a tight fit! Boy was I wrong. I will be sending these back today for a refund. If you want a good set of risers, do NOT buy these."