Simpson CSD25400 1/4" X 4" Countersunk Head Split-Drive Anchor - Zinc, Pkg 100The Split Drive anchor is a one piece expansion anchor that can be installed in concrete, grout filled block and stone. As the anchor is driven in, the split type expansion mechanism on the working end compresses and exerts force against the walls of the hole. The Countersunk head allows for a smooth surface when attaching wood or light gauge steel to concrete and grout filled block surfaces. Installation: For Common Rafters: Drill a hole in base