As this bowling season is getting underway, along with it comes the new regulations on balance holes. Starting now all holes placed into a bowling ball need to be used for gripping purposes. Any hole not used to deliver the ball will need to be plugged before it can be used in any certified play.
Per the documentation posted by the National USBC:
The specification eliminating the use of balance holes will go into effect Aug. 1, 2020. Balance holes, also known as weight holes, are meant to correct static imbalance in bowling balls, but more recently have been used to change the design intent of balls. By allowing bowling balls (for balls weighing more than 10 pounds) to have up to three ounces of static side, thumb and finger weight – which is up from one ounce – and up to three ounces of top weight, there no longer will be the need for a balance hole to correct static imbalance in the typical ball layout.
The specification increases in static weights take effect Jan. 1, 2020, which will allow bowlers the opportunity to plug balance holes prior to the elimination of balance holes starting Aug. 1, 2020.
With the elimination of balance holes, bowlers may have up to five holes for gripping purposes and all gripping holes must be used on every delivery.
You can find this information along with a full write up in the link to the initial rule changes below.