HDG, BZP and A2/A4 Stainless – What’s the difference?

06 February 2018
The most common fixing finishes explained.

HDG (Hot Dip Galvanised)

Hot Dip Galvanising (HDG) is the process of dipping a product in molten zinc, bonding it with the steel to provide a strong protective layer. This is a preferred way of achieving an element resistant finish due to the cost effectiveness and low maintenance levels after installation.

However, it is important to remember that when cutting a galvanised product, you will likely cut through the protective layer into the unprotected metal. An easy way to overcome this is with zinc galvanising spray, which provides protection to the exposed area.

BZP – Bright Zinc Plated

The most common finish with the majority of fixings. BZP (Bright Zinc Plated) is a process that takes place in the manufacturing stage of the fixing at which point the standard steel or alloy product is coated with a thin layer of zinc using electric currents, to offer galvanising protection to the steel and prevent rusting or oxidation. This layer is very thin which, although making the steel resistant to moisture, will not prevent rusting or oxidation in an outdoor environment.

A2 & A4 Stainless Steel

For general use, Stainless Steel is a steel oxide with a minimum of 10.5% Chromium content. This Chromium adds a protective capacity to the steel, helping it to resist corrosion.

A2 Stainless (or ‘Type 304’) contains 18% Chromium, and 8% Nickel. While suitable for applications in an outdoor environment, A2 stainless can discolour over time. It is resistant to sterilising solutions and man made chemicals, and is used extensively in the food production/preparation industry.

A4 Stainless (or ‘Type 316’) contains the same 18% chromium and 8% nickel, but also includes 3% molybdenum which provides an extra resistance and amounts to the ‘A4’ or ‘Type 316’ grade.