This paper reports on the development of wood screws that can be used for soft and light wood like Obisugi (a variation of Japanese cedar). The idea of taper screws came from the shape of traditional Japanese nails, and new wood screws in a taper shape were devised. We designed one parallel screw and six taper screws. Test results revealed that the taper shape of wood screws statistically improves withdrawal performance. Both Obisugi and European redwood were tested. The improvement in withdrawal performance as particularly remarkable in Obisugi.
