Flux brushes are used for apply flux to metal prior to soldering. They usually have firm to medium bristles and a metal handle. The are available at almost all craft stores as craft brushes. They are very cheap, running around $4 for a dozen or $15 for a gross (144). A good tip while working with flux brushes is to have a glass jar or baby food bottle to place the flux brush in between uses since the flux itself is corrosive and should not be on any work surfaces.