The Forster "Original", "Power" Outside Neck Turner Tool allows the reloader to make absolutely certain that their bullet is being released consistently from the case neck. At the point of ignition, the case neck must expand to allow bullet release. If the case neck is thicker on one side than the other, the thinner side will release the bullet sooner and causes a slight bullet-to-bore misalignment that can seriously impair accuracy. While hand-held neck turners center the brass case on a pilot the Forster "Original", "Power" Case Trimmer Outside Neck Turner turns case necks concentric to the cases true axis making for a more uniform thickness and exact outside neck diameter. These steel pilots, also called mandrels, are precision ground .002" to .0025" smaller than bullet diameter for optimum performance. Notes: Diameter listed in the description means this pilot is intended for a bullet of that diameter