Mitochondrial intermembrane chaperone that participates in the import and insertion of multi-pass transmembrane proteins into the mitochondrial inner membrane. May also be required for the transfer of beta-barrel precursors from the TOM complex to the sorting and assembly machinery (SAM complex) of the outer membrane. Acts as a chaperone-like protein that protects the hydrophobic precursors from aggregation and guide them through the mitochondrial intermembrane space (By similarity). Heterohexamer; composed of 3 copies of TIMM9 and 3 copies of TIMM10/TIM10A, named soluble 70 kDa complex. The complex forms a 6-bladed alpha-propeller structure and associates with the TIMM22 component of the TIM22 complex. Interacts with multi-pass transmembrane proteins in transit. Also forms a complex composed of TIMM9, TIMM10/TIM10A and FXC1/TIM10B (By similarity). The twin CX3C motif contains 4 conserved Cys residues that form 2 disulfide bonds in the mitochondrial intermembrane space. However, during the transit of TIMM9 from cytoplasm into mitochondrion, the Cys residues probably coordinate zinc, thereby preventing folding and allowing its transfer across mitochondrial outer membrane (By similarity). Belongs to the small Tim family.