The hole-unit on the Targaline Putting Aid comes with a 2.5" hole. The reason for this is simple, but very effective! You practice making perfect putts into the center of the hole. Putting to the center of the hole gives you confidence that you will putt on line, every time! The combination of the mirror and string provide instant feedback on your set up over the ball. By glancing back into the mirror to see the string and its reflection as one line on top of each other. This will ensure that your eye alignment is perfectly above the ball and the putting line, every time! Place 1 ball on each of the 4 acceleration marks. By not touching the next ball to the rear when you make a putting stroke, Targaline will teach you to accelerate through your putts. The putting guidelines help you square your putter and develop a consistent on-line pendulum putting stroke. At this point, all of the putting fundamentals come together in harmony, to create that consistent winning putting stroke from take-away into the follow through. A built-in, gravity controlled, ball return ensures that you can make putt after putt and the Targaline will send you back the ball.