The Otis 316-50 All Purpose Receiver Brushes (50 Pack) which allow you to choose the right brush for the right project. These brushes are the elite in cleaning those hard to reach places. They give you the ability to scrub places where carbon, powder and copper residue hibernate. The softest is the nylon bristled brush, followed by a slightly more aggressive blue nylon bristled brush. The most aggressive of Otis All Purpose Receiver Brushes is the bronze bristled brush.