The functions of tie rods are to resist the tensile forces resulting from the pressure of fresh concrete and to hold the two sides of wall form (sheathing) at the correct thickness. Wood or metal spreaders can also be used to keep the thickness of the wall constant. Ties can be broken off or unscrewed and remain an integral part of the concrete wall. Other types of ties may be removed for reuse, resulting in visible holes. Holes can be left visible or filled with mortar or ready-made plugs. Figure 6.3 shows several types of tie rods used in forming concrete columns and walls. Loadcarrying capacity for ties ranges from 1,000 to 70,000 lb (450 to 31,750 kg).