A general procedure is proposed for improving the self-consistency of binary mixed hard body fluid equations of state in both the small and large particle size ratio limits. The resulting equations correct both the total pressure and the solute chemical potential in a binary mixture with low solute concentration. The results are applied to the Bonded Hard Sphere (BHS) and Scaled Particle Theory (SPT) equations of state for mixtures of hard chains, to produce new SC-BHS and SC-SPT expressions with improved self-consistency. Comparison with computer simulation measurements of the chemical potentials of hard dumbbells in hard dumbbell fluids with solute-solvent sphere diameter ratios between 0 and 10 demonstrate the improved accuracy of the new equations. The improvement is most marked for SC-SPT, as the original SPT was nonself-consistent at both small and large solute sizes, while BHS was already self-consistent at small, but not at large, solute sizes. (C) 2001 American Institute of Physics.