Taper washers are designed for use on channel sections, underneath nuts nuts with tapered flanges to enable the bolt to fit square when tightened.
Self coloured finishes have no protection against corrosion, and are more suited for use in internal joinery applications. Self colour finishes have no definitive colour and can vary with the effects of natural oxidisation and weathering, from a bright zinc finish to a dark black colour. Before being used in exterior environments, they should be coated or painted with a protective covering.