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Bowling Ball Top Weight
The United States Bowling Congress (USBC) states that a bowling ball 10.01 pounds or more may have not more than three ounces difference between the top half of the ball (finger hole side) and the bottom half (side opposite the finger holes) after the holes are drilled.
A DoDo scale, the scale used to measure static weight of bowling balls, is needed to weigh the ball for top weight after drilling. If a ball has more than three ounces of top weight after drilling, an extra weight hole must be drilled into the ball to bring the top weight measurement below three ounces measured on the scale.
A ball used without any holes or indentations may not have more than one ounce difference between any two halves of the ball. This pertains to bowlers who use one or two hands and prefer not using finger holes for gripping purposes.
A top weight imbalance after a ball is drilled with gripping holes influences bowling ball motion. Top weight is created by core designs developed by manufacturers.
In modern terminology, top weight is a compatible measurement based upon the Radius of Gyration (RG) of a bowling ball.
RG can be described as a measurement by some manufacturers in a range from 2.460" to 2.800", but some companies have converted them to a 1-10 scale to help give the consumer a better frame of reference. These numbers describe the distribution of mass in the given bowling ball and RG is an account of the location of that mass inside the given bowling ball.
High RG numbers indicate that the ball's mass is distributed more towards the cover (cover heavy) which promotes length through the heads of the bowling lane. High top weight balls influence ball motion in much the same way.
Low RG numbers and low top weight measurements indicate that the ballâ€™s mass is distributed more toward the center (center heavy) which promotes an earlier roll through the front part of the lane.
Medium RG describes sufficient bowling ball skid length to reach the mid-lane before transitioning into the hook phase of overall motion.