The type of mass transfer that a primary star first initiates prior to its core collapse is a function of its initial mass. The transition at ∼10 M_⊙ leads to the knee in the distribution in the top-left panel of Figure 1. Mass transfer initiated on the donor star’s main-sequence is case A, while case B corresponds to expansion during the Hertzsprung gap, and case C occurs after the onset of core helium burning. Primary stars below ∼10 M_⊙ mostly initiate case C mass transfer, while more-massive stars initiate case A or B mass transfer. The top axis shows the main-sequence lifetime corresponding to the initial primary mass for the average metallicity of m11h as calculated by COSMIC.