Patent ID: 7861621

Claim:
A wrench comprising: a elongate body having a first end and a second end, a driving head connected on the first end and including a through hole which is composed of an accommodating hole and an engaging hole which communicates with the accommodating hole, the engaging hole including three engaging surfaces and three reception concavities defined in an inner periphery thereof and located about an axis of the engaging hole, the three engaging surfaces located alternatively to the three reception concavities, each engaging surface located on a convex and curved surface extending toward a center of the engaging hole and each reception concavity including two symmetric curved insides, the reception concavities each being adapted to accommodate one of protrusions of a star-shaped nut, a recess defined in a center of each of engaging surfaces and extending parallel to the axis of the engaging hole, each recess located between a first engaging portion and a second engaging portion which is located symmetrically to the first engaging portion, the reception concavity located at the conjunction between the accommodating hole and the engaging hole having one of two insides thereof connected to the second engaging portions next to it, the other insides of the reception concavity located at the conjunction between the accommodating hole and the engaging hole connected with a third engaging portion which has an identical shape as the first engaging portion, each recess including two insides and a bottom located between the two insides, a distance between the two insides adapted to accommodate one of protrusions of a star-shaped nut, a curved surface connected between the first/second engaging portion and the insides of each of the recesses, a smooth surface connected between the first/second engaging portion and each of the reception concavities, a space between the smooth surface and the reception concavity adapted to accommodate one of protrusions of a star-shaped nut, the adjacent first and second engaging portions having a common tangent line and three respective common tangent lines located on three sides of a hexagonal object, a distance defined between a center of an inscribed circle and a center of the accommodating hole, a maximum distance from the third engaging portion to the accommodating hole being larger than a maximum diagonal of the hexagonal object.