Reversible open end wrench having retaining property

A reversible open end wrench, comprising:

• a handle;
• a head, disposed at one end of the handle, the head having a first jaw, a second jaw and an extension section extending between the first and second jaws, the first and second jaws and the extension section defining a driving area therebetween for a hexagonal nut to receive therein, the driving area having an opening away from the extension section, the first jaw having a first engaging surface, a concave revolving surface and a distal end, the first engaging surface being adjacent to the extension section, a joint section between the first engaging surface and the extension section being formed with an abutting angle for receiving a corner of the hexagonal nut therein, the revolving surface locating between the first engaging surface and the distal end, the second jaw having a second engaging surface, the distal end having a short plane surface facing the second jaw, a horizontal distance between the first and second engaging surfaces being s, a horizontal distance between the short plane surface and the second engaging surface being no smaller than s;
• a retainer, disposed on the distal end and having a retaining end extending toward the driving area, the retaining end being movable between a first position and a second position;
• a resilient member for urging the retaining end back to the first position;
• wherein when the retaining end locates at the first position, a vertical distance between the retaining end and the abutting angle is bigger than 0.58 s, and a horizontal distance between the retaining end and the second engaging surface is smaller than s;
• wherein when the retaining end locates at the second position, the horizontal distance between the retaining end and the second engaging surface is no smaller than s;
• wherein in when the wrench is turned toward a specific direction, the nut received in the driving area is able to be clamped by the first engaging surface and the second engaging surface and to be driven to turn;
• wherein when the wrench is turned toward an opposite direction, a corner of the nut is able to revolve along the revolving surface, a corner of the nut is able to press the retaining end to push the retaining end from the first position to the second position.