1/4" NPT HEX SOC PIPE tapered PLUG PLATED.
With the NPT plugs you can remove the engine with out splitting the gear case.
Do not over tighten. Used on some of our 18.75 to 1 gear boxes.
One of the plugs needs to have a 1/16" hole drilled to Vent the pressure from building up in the gear case.
Below is a link for the "Vent" plug.
http://www.staton-inc.com/store/products/1_4_NPT_with_1_16_Drilled_Vent_hole-538-0.html