They don't HAVE to have three holes - people used to drill two holes and palm the ball, but it's easier to control the ball with three holes.
Because one is for your thumb one is for your index finger and the other for your middle finger and because if there was one forr all five fingers the ball would most likely spin when thrown
3. two fingers, one thumb *unless ball has a balance, or weight hole to make the ball USBC legal.
There is usually 3 holes in a Ten Pin Bowling Ball. 1 large hole for your thumb and 2 smaller holes for your middle and ring finger. Some bowlers may have different numbers of holes based on their bowling style.
Start by drilling a round "pilot" hole, then shape it with an end mill.
We can approximate the radius of a bowling ball to be about 26.7", the formula for calculating the volume of a sphere is (4/3)*pi*r^3 ,so the volume of our bowling ball is 79730.12 cubic inches
3 holes in a bowling ball
In tenpin bowling, bowlers who are having difficulty with release, usually related to the ball sticking on the thumb, will sometimes have a very small hole drilled just below the thumb hole, at angle that enters into the lower part of the thumb hole. This is to allow air into the lower region of the thumb hole and prevent a vacuum from taking hold.