A core element of an investment core for use in a casting process used to produce an airfoil includes an investment core body, an extension connected to and protruding from the investment core body, and a connection portion connected to the investment core body and to the extension. The investment core body comprises a ceramic material. A shape of the extension comprises a tube with a centerline axis passing through a center of the extension. A shape of a cross-section of the extension taken along a plane perpendicular to the extension centerline axis comprises an ellipse. The extension is connected to the investment core body by the connection portion.