SM series of sub-Electric insulators classified Class A (copper nut is 1.5 times the thickness C grade copper nut, torque and tensile strength of the C-class doubled For retardant please specify.) Class B (for iron-plated nuts nickel, torque and tensile strength is a double A-level recommended) Grade C (for thin copper market is the most common nuts, the price advantage, the proposed less stringent requirements on the quality of customer use) Note: When ordering please indicate the specifications you want, in seconds, to provide you with high-quality high strength SM51M8 insulators, unknown, please call or contact us online QQ or HC sub-Electric sincerely cooperate with you, rest assured purchase, look forward to your arrival sub-Electric SM Series Insulator classified Class A (copper nut is 1.5 times the thickness C grade copper nut, torque and tensile strength are C-level doubled For retardant please specify.) Class B (for iron nut nickel plated, torsion and tensile strength is a double A-level recommended) Grade C (for thin copper market is the most common nuts, the price advantage, the proposed less stringent requirements on the quality of customer use) Note: When ordering The specifications indicate that you want, in seconds, to provide you with high-quality high strength SM51M8 insulators, unknown, please call or contact us online QQ or HC sub-Electric sincerely cooperate with you, rest assured purchase, look forward to your arrival