I copied this from the ebonite site.
Axis tilt and axis rotation deal
with the angle at which the ball is revolving. The ball revolves on two planes: 1) horizontal, and 2) vertical. The angle of the ball's revolutions dictates the resistance to forward roll. Resistance to forward roll is synonymous with skid, delaying the breakpoint of the ball. The breakpoint is the point on the lane where the ball starts to make its move to the pocket.
Axis tilt is the vertical angle at which the ball rotates. Axis tilt is what is commonly known as spin. Axis tilt is determined by the position of the thumb during the release. If the hand turns too early, the thumb exits on top of the ball. Bowlers with a high degree of axis tilt will be able to see the top of their hand during the release and follow through. Being able to have the thumb exit at the bottom of the down swing minimizes axis tilt.
Axis tilt will induce skid and reduce the amount of backend hook potential. With the core rotating in a more vertical fashion, oily lanes will be the enemy, drier lanes its friend.
Axis rotation is the horizontal measure of the angle of the ball's revolutions. It is also determined by the release. It is the release position of the fingers that dictates the amount of axis rotation. Axis rotation is commonly known as side roll. When the fingers exit the ball in a 6:00 position, the ball is sent into an end-over-end roll. This is known as 0 degrees of axis rotation, the absolute minimum. This ball will have no chance of hooking, regardless of the amount of revolutions, ball speed, and lane conditions. The ball will have immediate forward roll. Think of it as being behind the wheel of a car with the steering wheel straight. The tires will face in a north-south direction. The car will go straight, not being able to negotiate a curve in the road.
If the fingers exit the ball in a 3:00 position, caused by a rotation of the hand in a counter-clockwise direction, 90 degrees of axis rotation will result. This will give the ball a tremendous hook angle when it encounters friction. This is similar to being in that same car. However the steering wheel is now turned so that the tires are angled to the left. When the accelerator is engaged, the car will **** violently to the left. (For lefthanders, the fingers will exit the ball at a 9:00 position, the hand rotates in a clockwise direction, and the car wheels would be pointed to the right).
Most players have a finger exit somewhere in between 0 and 90 degrees. The halfway point, 45 degrees, will see the fingers exit the ball at 4:30 at the release point (7:30 for lefthanders). This is the most versatile release position. Please consult the Surface Friction Guide, True Grit, for pictures of axis rotation and axis tilt.
Axis rotation also will cause the ball to skid further but, unlike axis tilt, will cause a dramatic hook angle at the breakpoint. 90-degree axis rotation is often quite uncontrollable at the breakpoint. High degree of axis rotation players will also tend to like drier lanes; minimal axis rotation will tend to like more oil.
The ball, as it is rolling down the lane, will lose axis rotation due to encountering friction. The rate at which the ball loses axis rotation (side revolutions turning into end-over-end revolutions) will be determined by the initial axis rotation, the amount of ball speed, the amount of axis tilt, and the amount of oil on the lane. For the best carry percentage, we want the ball to lose axis rotation (enter into an end-over-end roll) just as it enters the pocket. This will give a strong angle of entry into the pocket and the proper amount of deflection.
Your Pro Shop
technician will be able to assist you in determining your axis tilt and axis rotation. While it is not necessary to know the exact angle, knowing whether you have low, medium, or high amounts of each will make understanding your ball's reaction easier.