Abstract: A decking tool is disclosed which has a tool body (12) having side edges (12b). A detachable spacer bar (310) having spacer plates (25) is removably connected to the body (12) by holes (311) and stems (305) and wing nuts (306). The spacer plates (25) have parallel side edges (320) and tapering surfaces (321) for location between decking boards to space the decking boards apart. The spacer plates (25) are spaced apart by a distance corresponding to the width of the decking boards. The spacer bar (310) can be replaced by another spacer bar which has plates for different spacing to suit different sized decking boards. One of the edges (12b) forms a guide for a nail gun to facilitate nailing of the decking boards to floor joists.