Flat brushes are used to apply lubricant to chains and other moving surfaces.  The whisking action of the bristles evenly distributes the fluid as it reaches the contact surface.  Brushes can also help prevent dirt build up.

This Flat Brush features a standard holder with a 1/8" female NPT inlet to attach directly to a supply line.  The bristles are stainless steel (nylon is also available, see part number A2087-5).  

A replacement brush that slides into the holder is readily available.