This is a Dead Center Hole Locator for Locating Servos and Engine Mounting Holes. Great Planes Dead Center Hole Locater is a tool that should be in every modeler's toolbox. The tool is extremely easy to use. Simply press its self- centering alignment cone into the mounting hole with the engine positioned on the motor mount, and give the handle a few turns, the sharp drill tip leaves perfectly centered marks every time! Specs: One dead center hole locating tool, with drill size guide on back of package. One clear protective plastic tube. Tool is 6.75" in length to reach into cowls.