The Toro 21" walk behind aerator features an easy to use hydraulic drive system that moves in forward and reverse. The frame is built with 10 gauge steel and provides a low center of gravity for excellent side hill stability. This aerator has been designed to be able to turn with out needing to raise the tines. It uses a Kawasaki gas engine and can travel up to 4 miles per hour in forward and 2.2 miles per hour in reverse. The Toro 21" aerator uses 36 tines that can aerate up to 3-4 inches deep and can finish an acre of land in an hour. The width of the machine is 31.5 inches and it can aerate 21 inches wide with each pass. (Side note: the black foot bar on the bottom back of the machine no longer come on new aerators) Call Trey Willis at 703 919 5291 for more information on this aerator.