... : heat transfer;2, the fin-tube type: DR (extrusion type), L (winding type), high frequency welding;3, the fin-tube material: 1, base ... and so on. 2, fin: aluminum (extruded type or wound type), steel (wound type, high frequency welding), copper (winding type).4, finned tube size ... : 1, base tube: OD16, OD19, OD1 ", OD38; 2, fin: OD34, OD44, OD57 ...