For radially symmetric β-barrels the number of permissible values of S/N is a function of the number of strands per radial unit cell (s/uc is the number of strands per subunit for Type 1 structures and twice the number of strands per subunit for Type 2 structures). The black rectangles indicates that the S/N value is permissible. When N ≥ 10, values of the tilt angle, α, and D/N remains relatively constant for any given value of S/N.