What Finish
​
What is a Finish
​
The finishes on fasteners are wide and varied but essentially it is an anti-corrosion or decorative external layer. The number of modern finishes is quite astounding, measure in their hundreds and cover everything from look through to anti-corrosion. It is not possible to cover them all here so we will limit it to what is a finish and finishes that we sell.
​
A finish can describe the manufacturing process of making the fastener, the coatings applied to it, the aesthetics or look or all three together. It can be specifically named in a standard, the name of a process or plating, or it can just be a common name used by different groups of people that use the fastener that changes from country to country. We have chosen the look of the finish, its aesthetic, to be more important to our client’s than a name that is used in a standard or industry. The finishes we list give the same look regardless of process or standards.
​
What Period
​
Like style the time period makes large changes to the look of plated objects. Most plating patinas over time, it's colour dulls but the type of plating is still recognisable. Putting different types of plated fasteners onto a vehicle for example is functionally fine but may not give the look that is required.
​
If you are intending to restore an item then using a plate that gives the same look as the original is an advantage but some plate processes such as cadmium are no longer available due to health and safety protections. Although using the same plate on all the fasteners on a item will give a consistent look.
​
Stainless steel gives a great look and is very useful but care should be taken if the plate or metal types differ as unplated metals can cause galvanic corrosion.
​
What is Black or Bright
The names, concepts, and meanings of some of the finishes have changed over the last 100 years or as fasteners have become standardised. A black bolt described in the 1909 British Standard (BS) 28 is like a bolt from BS1083 blackened by the hardening treatment. Although neither looks like a yellow coloured, passivated bolt from the 2001 standard BS4190 ISO Metric Black Hexagon Bolts yet all are called black.
​
The phrase black bolt in a standard refers to the manufacturing process of the steel used rather than the finish of the bolt itself. When red hot steel has been drawn through dies or passed through rollers and then cooled it has a blackened appearance from oxidisation. It can then be forged, stamped, or pressed, have holes or threads cut and still have blackened oxidised areas.
A self-coloured fastener is also coloured black from the heat treatment of the hardening process but it is not a black fastener.
​
Bright steel is steel that has been worked again when cold, such as by drawing through dies or passing through rollers. The black oxidised layer is removed due to the process leaving the steel with a bright look. The steel could then be cold forged into a bolt, nut, etc and still retain the bright look.
​
A Bright finished fastener is one that has been machined on all surfaces or has a finish on the surface produced by bright drawing and regarded as a machined finish.
​
Different Finishings
Bright Zinc Plated (BZP)
​
Whilst zinc plating has been around since the 1800’s, the 1930’s brought in bright zinc plating. Although brighter than zinc it did not become widely used as a replacement for cadmium plating until the new processes in the 1960’s made the plating even brighter and more similar to a chrome.
It is far more eco-friendly than cadmium plating, leaves a more modern shiny, silvery surface on a fastening and is very thin, removing problems with thread tolerances. It provides a long-term tarnish protection. Most modern fastenings are produced in BZP.
​
Cadmium
​
Cadmium plating was used from the 1920’s. It has outstanding anti-corrosion properties and yet still thin enough not to affect the strength of the bond of threads mating together or how they fit together. Steel when newly cadmium plated looks like a very light grey that gets darker over time.
​
Unfortunately it is toxic and harmful and its use is now limited to aerospace and approved uses.
​
Coated
​
Coating using paint or powder is another finish that provides good long term anti-corrosion or tarnish resistance. The coating can be coloured or clear. Historically it is normally limited to washers and the heads of fastenings for decorative appeal because of the thickness of the coating. Hand painting or spraying for small batches of fasteners using modern thin film metal paints provides similar protection and decorative appeal. However, with modern materials the fastener can be completely covered in colour using PTFE fluoropolymers such as Xylan or Teflon. These polymers also have fantastic lubrication properties which means that the coating does not come off easily when the fastener is installed.
​
Galvanised
​
Hot or cold zinc galvanising provides the best long term anti-corrosion protection. Unfortunately, both processes leave a thick layer of covering on the surface that interferes with thread tolerances. It is more suitable to large fastenings where there are greater thread tolerances. It is possible to provide good galvanised small fastenings, but the care must made in their design to ensure that the tensile strength of the joint between fastenings is maintained.
​
Self Coloured
​
The surfaces of these fasteners are customarily coloured a dull black from the heat treatment used to harden the metal. This finish is not named in the older, Imperial standards as it was expected that any heat treated, un-plated or uncoated fastener would have this colour.
​
Electro-tinned
​
Applied to smaller steel, brass or copper fasteners to provide good conductivity without oxidisation.
​
