Ratio of the de-projected semi-major axes of outer and inner rings versus bar torque parameter (top panel), gravitational torques evaluated at the bar end (central panel), and the bar maximum m = 2 Fourier amplitude (bottom panel), shown as in Fig. 9. The red solid circles correspond to the few galaxies in our sample hosting outer (pseudo-)rings of type R₁ or R₁R₂, according to Buta et al. (2015).