Chain strengths are expressed as grades followed by a number. The letter used varies with countries but the strength of the chain remains the same.

The United Kingdom uses “U”, France and Spain uses “Q” and the Scandinavian countries use “K”. The number relates to the type and hence the strength of the steel. U1 grade is mild steel, U2 is a high tensile steel and U3 is a special heat treated steel.

These grades are normally only used within the shipping industry as the oil industry demands even greater strengths for the chain used.

The original grade designed for the offshore industry was ORQ (Oil Rig Quality). Although this chain is still in use it has been superseded by new grades such as Rig Quality 3 and Rig Quality 4. These grades were introduced by the classification societies in order to standardise quality.

The same grades also apply to the joining links that may be used with the chain. Tables showing the various strengths of chain are shown overleaf.