def get_mass_spin(bank, tid):
    """
    Helper function

    Parameters
    ----------
    bank : h5py File object
        Bank parameter file
    tid : integer or array of int
        Indices of the entries to be returned

    Returns
    -------
    m1, m2, s1z, s2z : tuple of floats or arrays of floats
        Parameter values of the bank entries
    """
    m1 = bank['mass1'][:][tid]
    m2 = bank['mass2'][:][tid]
    s1z = bank['spin1z'][:][tid]
    s2z = bank['spin2z'][:][tid]
    return m1, m2, s1z, s2z