Brushes are a compact, low profile design. The benefits of this design are a brush that follows chimney and flue contours, a brush that will easily reverse direction in the flue for easier cleaning, a brush that will easily negotiate angles and bends up to 90 deg., and a brush that results in a more thorough cleaning with less effort. 1/4-20 thread. Size: 4 In. Shape: Round Material: Fiberglass Thread Size: 1/4 In.-20 Thread Brush Size: 4" pack of 6