Spin magnitude χ₂ as a function of the initial orbital period for the full range of He star masses at low metallicities (Z_i ≤ 0.1 Z_⊙). The different symbols denote the different initial metallicities: circles, 0.1 Z_⊙; squares, 0.08 Z_⊙; upward triangles, 0.05 Z_⊙; diamonds, 0.03 Z_⊙; downward triangles, 0.01 Z_⊙. The dashed line shows the fitting formula for χ₂ as a function of the initial orbital period across all He star masses.