From DT Online
Plug Cutters are used to cut small pellets of timber which can be used to cover screw heads in Counterbored holes - as an alternative to Plastic Cover Caps. This is usually done to conceal the screws, by cutting a plug from a piece of matching timber and Grain, but plugs cut from a contrasting timber can be used for decorative effect.
Activity: It is possible also to construct a simple Dowel Joint by drilling through assembled pieces from the outside, tapping in dowels which are pre-cut to be a little shorter than the timber thicknesses and, while the glue is still wet, adding plugs to fill the recess from the end of the dowel to the surface. If care is taken positioning the dowels, and a suitable contrasting timber for the plugs is chosen, some striking decorative effects can be created which make a feature of the joints rather than trying to conceal them.