This Master Sweep brush head measures eight inches by eight inches, The square design makes this ideal for brick and masonry chimneys, The thread fitting is doubled swaged and plated for durability, The thread type is NPT, The round shaped bristles are tough and durable, The brush head features a double spiral spindle design, The oil tempered bristles are evenly distributed to form a rugged density, This brush will prove to more rugged and long lasting that comparably priced brushes, Master Sweep chimney brush head with an 8-inch x 8-inch square shape, Features a plated, double swaged 3/8-inch thread fitting of the traditional-course NPT-type thread, 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 bristles, creating uniform rugged bristle distribution, Master Sweep brush heads are long-lasting professional brushes that withstand the demanding abuse encountered by busy commercial chimney sweeps, Cleans chimneys more thoroughly and outlasts many comparably priced brush heads, SKU: RTLD177