Pre-Sale Starts NOW: $250 off Gravely Mow Like A Pro Sales Event April 27-May 10 on the ZT HD 48, 52, and 60. For homeowners who don't just want to mow their lawn but prefer to manicure it. The Gravely ZT HD is a residential mower often mistaken for a commercial unit. It has the power, durability, and high performance that lawn aficionados demand. Ask about our Service package offer: $479.