Challenge Europe recently announced the breadth of screw materials and finishes they work with on behalf of their industrial/manufacturing customers. The rational for using various materials or treatments/coatings is usually either technical or cost based.
This can vary from improved corrosion resistance by using stainless steel, zinc plated, zinc-nickel plated, galvanised, chrome plated, nickel plated or plastic screws. Improved electrical connection is often important and can be achieved by using brass screws or the copper plating of steel screws, in some instances silver plating is also an option. Where insulating properties are required many styles of plastic screws are now available.
Equally, light weight applications may suggest aluminium or titanium alloy fasteners. Appearance requirements may call for chrome plated screws – whereas cost considerations may demand self-colour steel or the more basic of the fastener range, dependent upon the application.
Good looks or ease of use are indeed frequent considerations, perhaps to minimise intrusion of the drive pattern into the head design or to match a desired drive style, e.g. hex, Torx or other with assembly equipment or desired torque values.