This is a Dead Center Hole Locator for Locating 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!

Includes

One dead center hole locating tool, with drill size guide on back of
package.
One clear protective plastic tube

Specifications

Tool is 6.75" in length to reach into cowls.