Bowling Ball Balance Hole
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Originally Posted: 11/21/11; Updated: 4/13/21
**2021 Update: Per USBC Official Rules, balance holes in bowling balls are now considered illegal and must be plugged in order to be used in USBC sanctioned events. For more info, please click here. **A
bowling ball balance hole is an extra hole (balance hole or weight hole) in a ball which is used to get the ball within United State Bowling Congress (USBC) specifications for imbalance (static balance). The maximum allowable diameter is 1-1/4" for USBC sanctioned play. A
bowling ball balance hole is a non-gripping hole drilled into the ball to adjust the static weights and to create dynamic influence.
The effect of static weights is extremely minimal on the ball's reaction. So the major influence in the effect of a balance hole lies in the effects that it has on the ball's dynamics, those forces affecting the ball when it is in motion.
The location of a balance hole with regard to the distance from the pin is the primary tool for altering the dynamics of the ball's core. The strength of the core is measured by the difference of the RG of the height of the core and the RG of the width of the core. This relationship is referred to generally as Differential. The greater the difference between the height and the width, the higher the Differential. Higher Differential results in more track flare potential, and will induce the ball to release energy quicker when the ball encounters friction. The breakpoint will be stronger and will increase the hook potential.
The USBC states that a
bowling ball may have no more than one (1) ounce of side weight after the holes are drilled. While many people have their opinions about whether or not this rule is valid, it is still in effect. You need a DoDo scale to weigh the ball for side weight. If you are over one (1) ounce (we recommend 3/4 ounce) then use the guide below to help determine what size drill bit you should use, and how deep you should drill.
It helps to know some of the information and specifications pro shop professionals use so you gain greater insight into the net affect balance holes have influencing bowling ball motion. This estimated bowling ball weight removal chart provided courtesy of
bowlingball.com assists the pro shop professionals in determining the size and depth of a balance hole to remove a given amount of weight and the size of a drill bit to accomplish the task.
Drill
Bit
Size Hole Depth in Inches (Estimated)
0.500 0.750 1.000 1.250 1.500 1.750 2.000 2.250 2.500 2.750 3.000
19/32 0.119 0.178 0.238 0.297 0.356 0.416 0.475 0.534 0.594 0.653 0.713
5/8 0.122 0.184 0.245 0.306 0.367 0.428 0.480 0.551 0.612 0.673 0.734
21/32 0.135 0.202 0.269 0.336 0.403 0.470 0.538 0.605 0.672 0.739 0.806
11/16 0.148 0.222 0.296 0.369 0.443 0.517 0.591 0.665 0.739 0.813 0.887
23/32 0.157 0.235 0.313 0.391 0.469 0.548 0.626 0.704 0.782 0.860 0.939
3/4 0.176 0.263 0.351 0.439 0.527 0.615 0.702 0.790 0.878 0.966 1.054
25/32 0.191 0.286 0.382 0.477 0.573 0.668 0.764 0.859 0.955 1.050 1.146
13/16 0.206 0.309 0.412 0.515 0.618 0.720 0.823 0.925 1.029 1.132 1.235
27/32 0.238 0.356 0.475 0.594 0.713 0.831 0.950 1.068 1.188 1.306 1.425
7/8 0.250 0.375 0.500 0.625 0.750 0.875 1.000 1.125 1.250 1.375 1.500
29/32 0.263 0.394 0.526 0.657 0.788 0.919 1.050 1.182 1.313 1.444 1.576
15/16 0.273 0.409 0.546 0.682 0.819 0.955 1.092 1.228 1.365 1.501 1.638
31/32 0.300 0.450 0.600 0.750 0.900 1.050 1.200 1.350 1.500 1.650 1.800
1 0.325 0.488 0.650 0.813 0.975 1.138 1.300 1.463 1.625 1.788 1.950
1 1/32 0.350 0.525 0.700 0.875 1.050 1.225 1.400 1.575 1.750 1.925 2.100
1 1/16 0.368 0.553 0.737 0.921 1.105 1.289 1.474 1.658 1.842 2.026 2.210
1 3/32 0.388 0.581 0.775 0.969 1.163 1.357 1.550 1.744 1.938 2.132 2.326
1 1/8 0.400 0.600 0.800 1.000 1.200 1.400 1.600 1.800 2.000 2.200 2.4000
1 5/32 0.425 0.638 0.851 1.063 1.275 1.488 1.700 1.913 2.125 2.338 2.550
1 3/16 0.450 0.675 0.900 1.125 1.350 1.575 1.800 2.025 2.250 2.475 2.700
When a bowler delivers a ball, the bowler imparts four forces to the ball:
1. initial ball speed
2. initial rev rate
3. initial ball axis tilt
4. initial axis rotation
These factors, plus the location of the Positive Axis Point, describe a bowler’s delivery during ball motion testing. As the ball travels down the lane, it passes through three phases and two transitions. This motion happens as follows:
1. the skid phase (the first transition from skid to hook)
2. the hook phase (the second transition from hook to roll)
3. the roll phase
After choosing a given bowling ball with the given coverstock you perceive to match the lane conditions you are targeting, the static weight balance dynamic shifts in accordance with the drilling layout pattern after gripping holes are drilled into the ball. Use of a balance hole would be the final factor important in achieving the desired ball reaction. The drilling technique consists of the layout and the balance hole location and size (if a balance hole is desired).
Drilling a balance hole in your bowling ball will change the Differential ratio when the ball is in motion. Since the Differential ratio will influence the ball motion, you can control the degree of transition your ball makes as it travels through the mid lane and when it transitions at the break point down the lane. The larger the differential ratio, the more asymmetrical the bowling ball. Conversely, the smaller the differential ratio, the less asymmetrical the ball.
Varying degrees of longer transitioning (longer hook zone) ball motion can be obtained by choosing to drill an asymmetrical ball. Asymmetrical balls after drilling show a defined, angular motion. These balls can create more area at the break point and will respond to friction faster at the break point than symmetrical balls.
We hope this information helps you in understanding the purpose of a bowling ball balance hole and how it can affect ball motion. We recommend you consult your local pro shop professional when selecting a new bowling ball and a drilling layout and to determine if a balance hole will improve your ball motion.
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