Powers Fastening Innovations 05551 Spike Anchor 3/8-Inch by 3-1/2-Inch Mushroom Head Grade 8.2 Carbon Steel Pre-Expanded Anchor, 25 Per Box One Piece, tamper-proof anchor for use in concrete, block, brick or stone Formed with an "s" shaped configuration at the working end of the anchor to create an expansion mechanism Powers Fastening Innovations