Top figure: distribution of semi-major axis for the resulting outer (filled blue steps) and inner binaries (filled green steps) following the binary–binary scatterings. Bottom figure: eccentricity distribution of the outer and inner binary, using the same colour-coding as in the top figure. In both figures, panels from top to bottom refer to cluster velocity dispersion values σ_c = 5 − 10 − 15 km s⁻¹, respectively.