Our ALLIGATOR solid-wall anchors are the strongest anchors for concrete, brick, and masonry on the market. They outhold all metal, adhesive, and epoxy anchors of comparable screw size. The special shape of their heads and the anti-rotation fins prevent the anchor from spinning and countersinking into the wall. The anchors work even when they hit a hollow cavity in the wall. There is no need to replace with a hollow-wall anchor! The screw thread locks into the "teeth" in the anchor for vibration proof and shock proof holding.