New Archery Products ThunderBall™ Magnetic Nocking System is unlike conventional nock systems, this new magnetic nocking system virtually eliminates the effects of string torque and uneven nock travel for increased accuracy, better flight and deeper penetration. It is durable and installs in minutes. The ThunderBall™ Magnetic Nocking System has an index tab for fast and easy vane orientation and it fits most popular carbon and aluminum arrow sizes.