Twist Rod 40cm Pole diameter up to 16mm, suitable for voiles and lightweight curtains. Pole diameter 16-22mm, suitable for light to medium weight curtains. Pole diameter 25-28mm, suitable for medium to heavy weight curtains. Pole diameter up to 35mm, suitable for heavy weight curtains. Voile poles, suitable for voile curtains only. Tension poles, suitable for nets and voile curtains.