Powers Fasteners 5552 3/8 x 4 Spike Mushroom Head Tamper Proof Anchor Carbon Steel The SPIKE anchor is a patented, one-piece, tamper-proof vibration resistant anchor for use in concrete, block, brick or stone. Several head styles and anchor materials are available. The SPIKE anchor is formed with an s shaped configuration at the working end of the anchor to create an expansion mechanism. Since the anchor is pre-expanded, there is no secondary tightening operation required which greatly reduces the overall cost of an anchor installation.