The IOSSO AR-308/AR-10 Brush Kit (19110) comes with four brushes that are sized to close tolerance for precision cleaning of the AR upper assembly. The brush kit contains an Upper Receiver Brush, Bolt Carrier Brush, Chamber Brush, and .308 Bore Brush. The brushes are made with a fiber that is cobalt blue which is a stiffer grade of fiber that allows for back and forth action unlike traditional brass and bronze type brushes. The fiber lasts approximately 8 to 10 times longer than other brushes. The brush is wound tighter and has more fiber per inch than any other brush.