One-way wrench

1. Field of Invention A wrench includes a head, a gear, an engagement element and a bent spring. The head defines a circular space and a crescent space communicated with the circular space. The gear includes a plurality of teeth and is received in the circular space. The engagement element includes a concave face formed with a plurality of teeth and a convex face and is received in the crescent space. The teeth of the engagement element are engaged with some of the teeth of the gear. The convex face contacts a wall of the crescent space. The bent spring is received in the crescent space so that first a section of the spring contacts the wall of the crescent space and a second section of the spring contacts the engagement element. When the head is rotated in a first direction, the gear tends to rotate the engagement element relative to the head in a second position opposite to the first direction so as to enhance the engagement of the teeth so as to avoid rotation of the bead relative to the gear. When the head is rotated in the second direction, the gear rotates the engagement element in the first direction relative to the head since the convex face is not hindered via the wall of the crescent space, thus disengaging the teeth of the engagement element from the teeth of the gear, thus allowing rotation of the head relative to the gear.