There are several types of pool bridge - open, closed, rail, and what I call the over-the-ball bridge. For shots on the table that you have trouble reaching, there is also the mechanical bridge.
The easiest to use, and probably the most popular, is the open bridge. As shown above, this is formed by laying the bridge hand on the table with the fingers spread, pulling the four fingers back to form an arch with the knuckles in the air, and tucking the thumb up against the index finger. The cue shaft is supported by the "V" between the index finger and thumb. The height of the cue tip to the cue ball can be adjusted by raising or lowering the arch of the hand.
The closed bridge, above, provides a more secure grip on the cue shaft and is preferred by more advanced players. This bridge is formed in a similar way to the open bridge, with the difference being that the tip of the index finger and the tip of the thumb are held together to form a circle or loop. The cue shaft is held in this loop, and the index finger and thumb are squeezed around the shaft to support it securely, as the shaft slides through when shooting.
Shown in the above picture, the rail bridge is used when the cue ball is so close to the rail that there is no room to place the bridge hand on the table. The bridge hand is held above the rail and the tips of the fingers are placed on the rail, with the index and middle fingers placed the width of the cue shaft apart. The thumb is tucked up out of the way. The cue shaft is place directly on the rail between these two fingers and the stick is stroked in this manner.
When the cue ball is touching or very close to another ball, it may not be possible to use the open or closed bridge. This is when the over-the-ball bridge is used, as seen above.
This bridge is very similar to the open bridge, except that the palm of the hand is raised up off the table. This raises the "V" of the bridge that supports the cue shaft. The thumb is tucked up higher next to the index finger knuckle instead of along the shaft portion of the index finger. With the "V" higher, you are able to reach over a ball that may be in the way of the cue ball, and contact it with the cue tip to make the shot.
When the cue ball is right against the cushion, the cue tip must sometimes be raised, along with the butt end of the cue, to get the correct angle of attack on the cue ball. As shown above, the open or closed bridge can be used in this situation, depending on your preference.
Whichever of the pool bridge types you use, it is important to spread out the fingers that are touching the table as wide as possible, to provide the maximum support and stability. The bridge must not move at all while shooting, as this will negatively affect your aim and result in missed shots.
The mechanical bridge is usually made of plastic or aluminum and attaches to a spare cue stick. This device allows you to position the bridge near the cue ball, when it is not possible to reach the cue ball to shoot in the normal manner. It features grooves that are made to hold the cue shaft as it is stroked for the shot.
In the pictures above, the bridge on the left is made of aluminum and has a tight slip-fit over the shaft of the pool cue. On the right is a plastic bridge that slips over the end of the cue, and is secured with a screw.
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