This paper presents analytical results by the Finite Element Method (FEM) on the effect of the roller diameter and taper angle on the deformed shape in twist rolling. The twist rolling has newly been proposed by the authors for twisting sheet metals at target twisting angles. The feasibility of the new method was studied by the FEM [1] and the efficiency of the method was experimentally verified to a certain extent [2]. Twisted sheet metals are used as propellers in crafts and electric power plants, turbine blades and so on. The sheet metals are ordinarily manufactured by machining, of which productivity and yield ratio are low. The new method would drastically improve the productivity and yield ratio, compared to conventional methods. The unique points of the method are to use a pair of rollers, which consist of taper and straight portions and to position the rollers at a skew angle to the rolling direction. The dominant parameters are the taper angle, skew angle and the axial position of the rollers. The authors' previous research works clarified the effect of the roller-axial position on the twisted shape. However, the effects of roller diameter and taper angle are not clear. This paper shows the result of a series of numerical experiments by the FEM and the geometrical studies on the effect of taper angle and roller diameter. The twist angle must increase with the increase of the taper angle if the upper and lower rollers do not geometrically interfere with each other and the skew angle is kept at a certain value. However, the skew angle must be adjusted depending on the taper angle for the prevention of geometric interference. As a result, there is an optimum taper angle for attaining the highest twist angle and the optimum taper angle changes depending on the roller diameter. REFERENCES [1] Kumar, A., Makiyama, T., Kajikawa, S., Kuboki, T. Development of twisting method of sheet metal using taper roller, COMPLAS XVI, (2021) Paper No. 541. [2] Kumar, A., Kajikawa, S., Makiyama, T., Kuboki, T. Effect of roller axial position and thickness on a twisted angle in the twist rolling of aluminum alloy 1050 sheet metal, Metals, (2023) 13-2:Article Number 383.