On the full size boat there are a lot of hexagonal-headed stainless steel bolt heads left unpainted and on full view.  Mostly, they secure panels and vents along the wheelhouse side, engine covers and the like.  These are an important feature of the model and are represented by specially made dummy hexagonal headed bolt heads, made from brass and Nickel plated.  These enable you to achieve coloured panels with unpainted bolt heads with amazing accuracy and relative ease.