BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stop block device of a measuring tape, more particularly to a measuring tape capable of retracting the tape and increasing the buffer of stopping and blocking effect to prevent the shear force produced by excessive retracting speed. An improved structure of a stop block button constitutes a stop block effect by pressing down the button to improve the life of the measuring tape and the safety to user. 
     2. Description of the Prior Art 
     In general, a traditional measuring tape usually has an internal tape wheel having a concentric spiral flexible bracket coiled at the center of the wheel and a ruler coiled around the exterior of the wheel. A flange is disposed at the front end of the ruler, and the central section of the flexible bracket of the tape wheel sleeves through the central axle on the left external casing. A buffering stop block is disposed at the front end of the ruler, and latched into the front end of the bottom of the left external casing, and the other side of the buffering stop block is latched into the front end of the bottom of the right external casing. The right external casing has screws installed into the screw hole for securing the central axle at the left external casing and fixed onto a pillar to constitute a measuring tape. The operation of the traditional product is to pull the ruler of the measuring tape to an appropriate length for measurement. After the measurement is completed, the front end of the measuring tape is released and the ruler of the measuring tape will be retracted since the measuring tape has a coiled flexible bracket (with an action similar to the winding) and gives a powerful automatic retracting function. The longer the ruler is pulled, the faster is the retracting speed. If the measuring tape is made of metal plate, then it may cut the user&#39;s hand very easily. It definitely cause inconvenience for its use. Furthermore, if the retracting speed is too fast, the end of the ruler will impact on the buffering member with a large force. In general, the structure of the conventional buffering member usually does not have a good buffering effect, and thus cause the front end of the measuring tape to fall off, and makes the measuring tape unusable. 
     To make the measuring tape more convenient to use and practical, the inventor of the present invention with many years in the related field performing a series of researches and developments to enhance the stop block device of the measuring tape, and finally succeeds to invent the present invention. 
     SUMMARY OF THE INVENTION 
     The primary objective of the present invention is to provide a stop block device of a measuring tape, and such stop block device has a button for pressing downward to constitute a stopping and blocking effect in order to enhance the buffering effect and reducing the impact of the retracting ruler, and improve the safety and life of the measuring tape. 
     To make it easier for our examiner to understand the objective of the invention, its structure, innovative features, and performance, we use a preferred embodiment together with the attached drawings for the detailed description of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings, in which: 
     FIG. 1 is an illustrative diagram of the assembled structure of the present invention. 
     FIG. 2 is an illustrative diagram of the disassembled parts of the structure of the present invention. 
     FIG. 3 is an illustrative diagram of the right external casing structure of the present invention. 
     FIG. 4 is an illustrative diagram of the left external casing structure of the present invention. 
     FIG.  5  and FIG. 6 are illustrative diagrams of the stop block button structure of the present invention. 
     FIG. 7 is an illustrative diagram of the latch bracket structure of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In this detailed description of the preferred embodiments, it should be noted that like elements are indicated by the same reference numerals throughout the disclosure. 
     Please refer to FIG. 1 to FIG.  7 . The stop block device of a measuring tape of the present invention comprises a right external casing  1 , a left external casing  2 , a buffering member  3 , a wheel  4 , a stop block button  5 , and a latch bracket  6 . 
     The right external casing  1  is integrally made of a plastic material. A central screw hole  11  is disposed at the center of the inner layer of the right external casing  1 . A screw hole  12  is located at the front end of the lower edge of the inner layer, a tubular screw hole  13  is disposed at a rear end of the lower edge of the inner layer, and a screw hole  14  is disposed at the upper edge of the inner layer. The lower edge of the screw hole  14  has a circular latching axle hole  15  adjacent thereto, and the front end of the lower edge of the inner layer has two rectangular latch brackets  16  (only one latch bracket  16  is fully visible in the drawing Figures). A stop block  17  is disposed between the latch brackets  16 , adjacent the lower ends thereof. The stop block has a slanted surface  18  on its external side. The left external casing  2  is integrally made of a plastic material. A central axle  21  protrudes from the center of the inner layer of the left external casing  2 . A fixed screw pillar  22  protrudes at the front end of the lower edge of the inner layer. A fixed screw pillar  23  is disposed at the rear end of the lower edge of the inner layer. Furthermore, a fixed screw hole  24  is disposed at the upper edge of the inner layer of the left external casing. The lower edge of the screw hole  24  has a circular latching axle hole  25  adjacent thereto, and the front end of the lower edge of the inner layer has two rectangular latch brackets  26 . A stop block  27  is disposed between the latch brackets  26 , adjacent the lower ends of latch brackets  26 . The stop block  27  has a slanted surface  28  on its external side. 
     The wheel  4  has a centrally located concentric spiral flexible plate  41 . The wheel  4  has a ruler  42  coiled, a ruler head  23  is riveted to the front end of the ruler  42 , and each side of the wheel  4  has a respective wheel guard  44 ,  45  thereon. 
     The stop block button  5  is integrally made of a plastic material. The stop button  5  has a latch wing  51 ,  52  on each side of its middle section and two triangular stop block cones  53  protruding from the inner side of the stop block button  5 . 
     The latch bracket  6  is integrally made of a plastic material. The latch bracket  6  has a fixed axle rod  61  transversally disposed thereon, and a hollow latch groove  62  disposed at the middle section of the latch bracket  6 . The latch groove  62  has a slanted surface  63  at a bottom portion thereof. Furthermore, both sides of the bottom of the latch bracket  6  have a downwardly slanted stop and block surface  64 . 
     The central section of the flexible plate  41  of the wheel  4  is sleeved onto the axle  21  of the left external casing  2 . A buffering member  3  is latched to the front end of the bottom of the left external casing  2  with the ruler  42  extending therethrough. The fixing axle rod  61 , located at the top of the latch bracket  6 , is latched into the latch axle hole  25  of the left external casing  2 . A bottom side of the latch bracket  6  has a stop block surface  64  disposed between the two rectangular latch plates  26  at the front end of the inner layer of the left external casing  2 . The latch wing  51 , at the middle section of the stop block button  5 , is latched to the front edge of the inner layer of the left external casing  2 . The stop block cone  53 , at the center of the inner side of the stop block button  5 , passes into the latch groove  62  at the middle section of the latch bracket  6 . 
     Another side of the buffering member  3  is latched to the front end of the bottom of the right external casing  1 . The other end of the fixed axle rod  61  is coupled into the latch axle hole  15  of the right external casing  1 . The stop block surface  64  on the other bottom side of the latch bracket  6  passes between the two rectangular latch plates  16  at the front end of the lower edge of the inner layer of the right external casing  1 . The latch wing  52 , on the other side at the middle section of the stop block button  5 , engages the front edge of the inner layer of the right external casing. 
     A plurality of screws  7  respectively pass through the central screw hole  11  and screw holes  12 ,  13 ,  14  to secure the central axle of the left external casing  2  and the fixed screw pillars  22 ,  23  and fixed screw hole  25 , to construct an integral measuring tape. 
     In the measuring tape assembly of the present invention, the ruler  42  is pulled out to an appropriate length for use. When the ruler of the measuring tape needs to be fixed at a position, the stop block button  5  can be pressed down. When the stop block button  5  is pressed down, it forces the latch bracket  6  to be displaced downwardly, so that the mutual clipping relation of the stop block surface  64  on both sides of the bottom of the latch bracket  6  and the slanted surfaces  18 ,  28  gives the effect of fixing the ruler  42  and stopping retraction of the ruler  42 . 
     While the present invention has been described in connection with what is considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretations and equivalent arrangements.
A stop block device of a measuring tape includes a stop block button with an improved structure that displaces a latch bracket having stop block surfaces to press down on the measuring tape.