Front of Center (FOC) balance point is a very important factor in determining the accuracy of your arrows. If FOC balance point is below 8%, the controlling point of the arrow will move toward the nock causing the arrow to be inconsistent and less accurate. If FOC balance point is above 15%, arrow spine can be reduced causing arrows to dive. Adding weight to the point end makes arrow flight more consistent and increases penetration. Adding weight to both the point end and nock end of the shaft will increase overall arrow weight without altering dynamic spine. Importantly, these adjustments can be made in the field or on the range without removing the insert. Simply pull the nock and use the weight wrench NOT INCLUDED . Package of 12.