One Each Nylon, Blue Nylon and Bronze. Otis’ All Function Receiver Brushes permit you to select the best brush for the best job. These brushes are the elite in cleaning those difficult to reach locations. They offer you the capability to scrub places where carbon, powder and copper residue hibernate. These brushes are available in a range of different tolerances. The softest is the nylon bristled brush, followed by a somewhat more aggressive blue nylon bristled brush. The most aggressive of Otis’ All Function Receiver Brushes is the bronze bristled brush.