(Moore Maker) This heavy duty post driver lifts itself after each stroke! A spring-loaded piston inside the barrel strikes the post on the downstroke. This action results in a rebound that lifts the driver for the next down-stroke. Getting in time with this action-reaction will result in a speed of over 40 strokes/minute. Heavy duty steel construction with removable spring and piston. 2 1/2" inner diameter barrel, 32" long.