Basically it is a dummy propellor for hand rotating the engine in the overhaul stand during overhaul, Because the engine is too close to the ground you need to pull the handle out and reposition it every 90 degrees. It is not that different to the Pratt/Wright/Warner/Allison/etc equivalent tools though some have a fixed handle so you need to slide the tool off the prop shaft ever 90 to 120 degrees.