Correlations have been discovered which suggest that phases of the crystal structures A2, A15, C15, and D8b, that have Nb or Mo atoms occupying the chain sites in these structures, belong to a class having a common rigid band shape and having a common electron-phonon coupling mode responsible for T c. The latter is identified as associated with transverse vibrations of atoms situated on sites along close-packed chains in these structures. On the basis of these correlations and known interatomic potentials, optimum T c values may be predicted for hypothetical substances. NbMo2Be is predicted to form an A15 structure and to have an optimum T c = 30K.