“…Sibgatullin's integral method [12] of constructing the exact solutions changed that unpleasant situation drastically, and thanks to it we now have at our disposal various analytical solutions for a pair of interacting Kerr black holes separated by a massless strut which are suitable for the study of the thermodynamic length in the stationary binary systems. Thus, in our paper we are going to consider the configurations of two equal counterrotating Kerr black holes [13,14], of two identical corotating Kerr black holes [15,16], and also the binary system composed of generic Kerr black holes [15,17,18]. We have decided to analyze the configurations of equal counter-and corotating black holes separately from the general case because the thermodynamical properties of these particular two-body systems were already discussed earlier in the literature [19,20], however, using exclusively the general formulas of the usual double-Kerr solution [9] restricted to the subextreme case only and not elaborating the explicit form of the particular cases; besides, the thermodynamic analysis of the corotating case in [20] is essentially based on numerical calculations.…”