The new JK XD steering gear replaces the 70mm stock piston with a larger 80mm piston, giving it more turning torque to turn up to 37” tall tires without the need of cylinder assist. More material was added to the case in all mounting for sturdier base. Sector shaft diameter is increased from 35mm to 42mm for a 35 percent increase in strength. The JK-HD kit comes with a new factory drop pitman arm, nut and washer to match the newer larger sector shaft. Anyone with a Jeep JK running bigger than factory tires will want this bolt on upgrade on their must have list.