Master Sweep chimney brush head with a 12-inch x 12-inch square shape. * Features a plated, double swaged 3/8-inch thread fitting of the traditional-course NPT-type * Tough, durable round wire bristles. * Brush head has a has a heavy-duty double spiral 0.177 dia. spindle design. * The seven inches of fill is two on two high density oil tempered 22 gauge 0.0286-inch wire