Grain size distribution for a nonrotating progenitor with a mass of 20 M_⊙. The horizontal axis represents the grain size, while the vertical axis indicates the corresponding dust mass for each size bin, which is defined as in Eq. (3), with 50 bins. From left to right, the panels show results for an initial stellar metallicity of [Fe/H] = 0, −1, −2, and −3, respectively. In each panel, the solid, dotted, dashed, and dash-dotted lines correspond to the no-reverse shock (no-rev), rev1, rev2, and rev3 models, respectively.