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 tim-9/tin-9.1 and 3 copies of tim-10/tin-10, named soluble 70 kDa complex. The complex associates with the tim-22 component of the TIM22 complex. Interacts with multi-pass transmembrane proteins in transit (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 tim-9/tin-9.1 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.