Vallejo expands the range of Hobby Tools to include a wide selection of highest quality precision tools, designed to cover all the needs of modellers and hobby fans. Vallejo Hobby Tools - Glass Fiber Brush Refills (4 mm). The tools are useful for easy assembly or for the most complicated set up, and are indispensable in all quality modelling projects. The abrasive glass fiber pencil is ideal for accurate and rapid cleaning, de-rusting and surface preparation on a variety of materials. The propelling pencil action exposes more or less of the glass fibers. The shorter the fibers showing, the more abrasive the action.