IOSSO AR15/AR10 Upper Rec Brush Pack w/ Stud The IOSSO AR-15/AR-308 Upper Receiver Cleaning Brush 2 Pack (19121) comes with two brushes that are sized to close tolerance for precision cleaning of the AR upper assembly. 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 last approximately 8 to 10 times longer than other brushes. The brush is wound tighter and has more fiber per inch than any other brush.