Heavy duty taper lock bushing coupler. Shaft bore is 3.25" (3 1/4) inches, overall diameter is 10.5" inches and the keyway is about 7/8" inches. Overall it is about 4 3/4" inches wide. I believe it goes to a piece of concrete equipment or saw or some sort of landscape equipment. The following is printed on the side of it in paint RM- 140. Questions glady answered.