Abstract: A guide assembly mounted on a fastener driving tool locates the tool a predetermined distance from the edge of hardboard siding or a similar workpiece and assures that a fastener is driven into the workpiece the correct distance. The tool includes a housing having a nose defining a drive track and a driver blade for driving fasteners along the drive track into the workpiece. A safety member moves relative to the housing between a workpiece responsive position extending beyond the nose and an operating position, and a spring urges the safety member toward the workpiece responsive position. The guide assembly includes a yoke with a central portion adjustably mounted to the safety for controlling fastener penetration. A pair of laterally extending arms carry edge guides to locate the tool spaced from the workpiece edge in either of two different tool orientations. The edge guides are retractable so that one may be retracted when the other is used, or so that both may be retracted if neither is used.