A fastening tool has a tool body and a driver, the driver having a percussion head drivable generally vertically downward upon receiving a blow from a hammer. The tool includes a fastener head for apply a percussion drive in a generally diagonal direction to a fastener lodged in a strike position in the fastening tool. An elongate flexible transmission element moves in a track between the percussion head and the fastener head for transforming the vertically downward hammer drive into the generally diagonal drive to drive the fastener into the edge of a floorboard. The fastening tool can be used much closer to a finishing wall than known board fastening tools.