The cable consisted of seven copper wires, each weighing 26 kg/km (107 pounds per nautical mile), covered with three coats of gutta-percha (as suggested by Jonathan Nash Hearder), weighing 64 kg/km (261 pounds per nautical mile), and wound with tarred hemp, over which a sheath of 18 strands, each of seven iron wires, was laid in a close helix. It weighed nearly 550 kg/km (1.1 tons per nautical mile), was relatively flexible and was able to withstand a pull of several tens of kilonewtons (several tons).