Rutland MS-77 7 in. X 7 in. Square Master Sweep Round Wire Brush Head With .38 in. Npt Connector Master Sweep chimney brush head with a 7-inch x 7-inch square shape. Features a plated&#44; double swaged 3/8-inch thread fitting of the traditional-course NPT-type thread. Tough&#44; 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 bristles&#44;