The diameters of our brush's black-iron stems/heads are as follows: small = 1/16-inch, med = 1/8-inch, large = 1/4-inch. Phosphor bronze bristles are used on hard/soft/blued metals. The pencil-type design allows you to put your arm's force through the brush axis and into the brush head which is more force than possible when rotating a spiral bore-brush inside a chamber. More force means more cleaning friction. By achieving more force behind our utility brush, you remove stubborn rust, carbon deposits, oxide layers, other chemical corrosion, and embedded dirt or grime. Try one of our signature techniques, which is to use our Angle Brush to push a small patch section into spot to be cleaned. Our history is that we at BrushSmith/BoreSmith pioneered wire pencil brushes into the gun market in Summer 2005. They come in a slide pack with insert flyer.