Stainless Steel Coach Bolts: A2 vs A4

Stainless steel coach bolts are used where corrosion resistance matters. The two most common grades are A2 and A4, but choosing the right one depends on the environment and the job.

This guide explains the difference between A2 and A4 stainless steel coach bolts, where each should be used, and how to select the right option for site work.

What are A2 and A4 stainless steel?

A2 and A4 refer to different grades of stainless steel used in fixings.

A2 stainless steel – standard corrosion resistance, commonly used for general external applications
A4 stainless steel – higher corrosion resistance, designed for harsher environments

Key differences between A2 and A4

Feature	A2 Stainless Steel	A4 Stainless Steel
Corrosion resistance	Good	Higher resistance
Typical environment	Outdoor / general use	Marine / coastal / high exposure
Cost	Lower	Higher
Common use	Fencing, decking, garden structures	Coastal work, exposed structures, industrial use

When to use A2 stainless coach bolts

A2 stainless steel coach bolts are suitable for most external applications where basic corrosion resistance is required.

Fencing and gates
Decking structures
Garden buildings
General construction work

They offer a practical balance between cost and performance for standard outdoor conditions.

When to use A4 stainless coach bolts

A4 stainless steel coach bolts are designed for more demanding environments.

Coastal or marine locations
Areas exposed to salt or chemicals
High moisture environments
Long-term external installations

Important: In coastal or high-exposure environments, A2 stainless steel may not provide sufficient corrosion resistance. A4 should be used instead.

Choosing the right stainless coach bolt

When selecting between A2 and A4, consider:

The environment the fixing will be exposed to
The expected lifespan of the installation
The level of moisture or chemical exposure

For general outdoor work, A2 is usually suitable. For harsher conditions, A4 is the safer choice.

Coach bolt sizing and selection

Stainless steel coach bolts follow the same sizing as standard coach bolts. For help choosing the correct size, see our coach bolt size guide.

For technical dimensions, refer to our DIN 603 coach bolt guide.

Available stainless steel coach bolts

View our current range of stainless steel coach bolts:

Stainless steel coach bolts

Important: Whilst zinc plated coach bolts generally come supplied with nuts, stainless steel coach bolts do not. Be sure to add stainless steel nuts to your order if you need them.

Frequently asked questions

What is the difference between A2 and A4 stainless steel?

A4 stainless steel provides higher corrosion resistance than A2 and is used in more demanding environments.

Can A2 stainless be used outdoors?

Yes. A2 is suitable for most general outdoor applications.

When should A4 be used?

A4 should be used in coastal, marine or high exposure environments.

Are stainless coach bolts as strong as high tensile?

Stainless steel prioritises corrosion resistance rather than strength. For higher load applications, high tensile bolts may be more suitable. A4 stainless is sometimes called high tensile stainless steel, but this is not strictly true as it is not as strong as 8.8 grade high tensile steel.