The Strong-Drive SD Connector screw is specifically designed to replace nails in certain Simpson Strong-Tie connectors and is the only screw approved for that application. The load-rated SD screw has been tested and approved for use in many popular Simpson Strong-Tie products. In certain applications screws are easier and more convenient to install than nails, and the single-fastener load values achieved by the SD screw exceed those of typical 10d common or 16d common nails. In addition, the galvanized coating makes the SD screw ideal for interior and most exterior conditions. 1/4 hex head.