A wrench is a tool used to secure nuts and bolts. Some wrenches have separate straight ends that match the part to be stretched; These tools are open-ended wrenches in different sizes to accommodate specific sizes of bolts and nuts. Nuts and bolts or wrenches come in different shapes and sizes and are used to secure, rotate, tighten and loosen objects such as pipes, pipe fittings, nuts and bolts. Pipe wrenches, which are used in pipes to secure round (cylindrical) objects.