Nano-diamond and a-C(:H) material beta factors, β = F_pr/F_grav, the ratio of the radiation pressure and gravitational forces for nano-diamonds (cobalt), aliphatic-rich a-C:H grains with E_g = 2.67 eV (grey), and aromatic-rich a-C grains with E_g = 0.1 eV (black) 10 AU from HR 4049 (short-dashed), Elias 1 (long-dashed), and HD97048 (solid). The data point colour coding is for the same sizes as in Fig. 1.