1.  Field of the Invention
The present invention relates to sockets for wrenches and more particularly to an improved socket which is able to adapt itself to an open end of one of a plurality of wrenches of different sizes. 
2.  Description of Related Art
There are a variety of wrenches (e.g., open end wrenches, box end wrenches, combination box and open end wrenches, flare nut wrenches, etc.)  commercially available.  Further, a wide variety of sockets in cooperation with the wrenches are available.  As shown in FIG.  1, a conventional socket 1 comprises a lower connecting section 2 in the shape of cavity having a section of hexagon, the connecting section 2 being adapted to couple to an object to be fastened or unfastened, and an upper coupling section 3 in the shape of cavity having a section of square, the connecting section 3 being adapted to couple to a protrusion 5 on the bottom of a wrench 4.  However, the socket 1 may be useless if a wrench having a conformed protrusion is not immediately available.  This can bring inconvenience in use. 
For increasing convenience of socket in use, there have been numerous suggestions in prior patents.  For example, Taiwanese Patent Application No.  87208151 entitled “Socket for Spark Plug” is shown in FIGS.  2 and 3.  The socket 6 comprises a cylindrical connecting section 7 at one end having a cavity therein, and a projected actuation block 8 at the other end, the actuation block 8 having a section of hexagon.  Further, a recessed coupling section 9 having a section of square is formed on top of the actuation block 8.  An open end wrench 10 can hold the actuation block 8 in its open end for working.  However, only an  open end wrench having a conformed size is adapted to hold the actuation block 8 in its open end.  In other words, open end wrenches other than the above size are useless (i.e., incompatible).  Thus, use convenience is still not improved. 
Another Taiwanese Patent Application No.  87220532 entitled “Socket Having a Hexagonal Actuation Block” is shown in FIGS.  4 and 5.  The socket 11 comprises a cylindrical connecting section 12 at one end having a cavity therein, and a projected actuation block 13 at the other end, the actuation block 13 having an arcuate, tapered lower end and a section of hexagon (i.e., there are six curved upper bearing sides 15 and six curved lower bearing sides 14).  An aperture 16 is formed in each bearing side 15.  Further, a recessed coupling section 17 having a section of square is formed on top of the actuation block 13.  A wrench 18 can hold the actuation block 13 in its ratchet box end in which the socket 11 is adapted to adjust its angle by disposing the lower bearing sides 14 and the apertures 16 in different orientations.  However, only a ratchet wrench having a conformed size is adapted to hold the actuation block 13 in its box end.  In other words, ratchet wrenches other than the above size are useless (i.e., incompatible).  Thus, use convenience is still not improved. 
Thus, it is desirable to provide a novel socket for adapting itself to an open end of one of a plurality of wrenches of different sizes in order to overcome the above drawbacks of the prior art.