This cleaning brush has been designed in the shape of a pencil and holds fibreglass brush strands which are 4 mm in diameter.  Fibreglass Bristle PCB and Flux Brush, 4mm Diameter. The bristles can be moved accordingly in and out of the holder, by rotating the end knob clockwise and anticlockwise. This function is ideal for protecting the brush and keeping it clean when it is not being used, as well as having the bristles at the required length for the job in hand.