GearWrench 2490D 3-1/4” Heavy-Duty Engine Cylinder Flex-Hone GearWrench 2490D 3-1/4” Heavy-Duty Engine Cylinder Flex-Hone produces a controlled surface condition unobtainable by any other method, each abrasive globule is attached to high density nylon filament to enhance durability, a high percentage plateaued surface is produced free of cut, torn or folded metal.