Masses of Star 1 (x-axis) and Star 2 (y-axis) at core helium depletion for systems with q_i = 0.9, 0.7 (plotted as triangles and squares respectively). Models in the Standard Grid (without enhanced mixing) are marked in black, those in the Enhanced Grid (with enhanced mixing) in green. For clarity systems with q_i = 1 are not plotted as they remain at their initial mass ratio. The grey dotted lines show various mass-ratios as marked. Red, blue, yellow and purple stars represent measured progenitor masses of gravitational wave events GW170729, GW170823, GW150914 and GW170818 respectively (Abbott et al. 2016; The LIGO Scientific Collaboration & The Virgo Collaboration 2019).