def _get_bond_type_key(bond,
                       sigma_conversion_factor,
                       epsilon_conversion_factor):
    """Get the bond_type key for a bond"""
    return (
        round(bond.type.k * (sigma_conversion_factor ** 2 / epsilon_conversion_factor), 3),
        round(bond.type.req / sigma_conversion_factor, 3),
        tuple(sorted((bond.atom1.type, bond.atom2.type))),
        bond.atom1.residue.name, bond.atom2.residue.name
     )