The chart covers BH masses from smallest 10+10 solar masses to 2X times 2.15E+6 Suns similar to the total mass believed to exist at the center of our Milky way Galaxy. Two individual BH's (gray shadowed) illustrate the locations of the two individual event horizons for condition of Zero OVERLAP (tangent EH's).
NOTE: There is no significance to the vertical CG positions of shadowed gray BH's (shown at 10 Hz); Think of the right hand Shadow fixed at the 100% position; Move the Left Shadow to the right or left. The X-axis Overlap number below the Left CG is the Overlap (%) for that position. The figure is shown at Zero Overlap, move the left Shadow CG to the right (on top of right Shadow) to produce 100% overlap.
The shadowed regions represent full range of solar (any) mass BH's since the chart X-axis is expressed in units of RSCHWARZSCHILD. This can be seen in the three bold orange columns (for different masses) of the table. The BH 85.316% Overlap points where Newtonian VTANGENTIAL = 'c' are filled black and show 1.000 in the table data.
For 100% OVERLAP the two singularities would be considered Merged and only one gray shadowed area would show, HOWEVER, it would be twice the diameter shown since the one singularity would have twice the mass of either one of the two prior to the merger. AND conservation of angular momentum would demand that it be a Kerr Black hole. There is no attempt to show the combined event horizon. Page Un_Equal_Binary shows the dynamical Event Horizon profile for an Un-Equal Elliptical Binary (at the bottom of that page). The next link Elliptical_BH_Binary shows the dynamical event horizon for several Equal-mass Elliptical BH's.
Notice that a 10SM+10SM Binary would need a 30% EH Overlap to produce a 1000 Hz spin rate. On a larger scale, If our galactic BH was a Binary with 0% Overlap the spin rate would be 0.0015 Hz and would take about 11.1 minutes to make one revolution.
This tabulation, in addition to spin rates shows another interesting result: The tangential velocity of the BH singularities is a function only of the fractional RS distance from the Barycenter. Singularity (v/c, Beta) velocity versus Overlap is independent of mass units. At about 85.316% Overlap the Newtonian relativistic velocity would be equal to 'c'. See Relativistic_Corrections to see actual velocity and relativistic mass increase (Gamma=1.618...).