A hand tool includes a body which is a cylindrical body and has a hexagonal mounting portion defined in one end thereof. The mounting portion includes six side faces, and each side face includes a function portion which is connected between two contact faces. Six curved recess are defined alternatively between the side faces. Each function portion includes two consecutive V-shaped recesses. The first length is defined between two respective outer ends of the two contact faces of each side face. The mounting hole is defined by an imaginary hexagonal column which includes an axis and six sides. Each side of the imaginary hexagonal column is located corresponding to each contact face. The length of each side is defined as the third length. The first length is 0.5 to 0.65 of the third length.