The weight of a bowling ball is not always evenly distributed in the sphere. ABC rules allow a ball to vary 3 ounces from the drilled top half to bottom half of a ball, and one ounce from the left to right side. Before resin balls, these weights were used to subtly change the roll pattern of a ball. A ball that had higher top weight would tend to go longer before hooking; a ball with bottom weight would tend to roll earlier. Although still used in ball drilling layouts, it is less important with the modern ball.

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