A wrench includes a handle having a driving head which has a clamping hole. The driving head has a top surface and a bottom surface. The outer periphery of the top surface is tangent to an inside of a first circle and the outer periphery of the bottom surface is located on a second circle. The first circle is larger than the second circle. The second circle is larger than the clamping hole. When the first and second circles are projected on a horizontal plane, the second circle is located within the first circle and is tangent to the second first circle at a tangent point. The clamping hole and the first circle are located on a common axis which is located on a vertical plane. The two respective centers of the first and second circles and the tangent point are located on the vertical plane.