A chain marked with a 4 is identified as what kind?

A Grade 43 High test.

explanation

Grade 43 High Test chain is commonly used in the trucking and transportation industry for load securement purposes. It is known for its strength, durability, and resistance to wear and abrasion. The "43" in Grade 43 refers to the minimum tensile strength of the chain, which is approximately 43,000 pounds per square inch (psi).