Which of the following types of chain is not recommended for towing?

Proof coil chain is not recommended for towing due to its design and strength characteristics. This type of chain is typically made from low to medium carbon steel and is primarily intended for applications such as securing loads and lifting, rather than towing. It does not have the strength or durability required to handle the significant forces and stress involved in towing operations.

In contrast, alloy chains, transport chains, and high test chains are specifically manufactured to withstand the additional stressors that come into play during towing. Alloy chains are made from a stronger material, which allows them to handle higher loads. Transport chains are designed for securing loads during transportation and are engineered to be robust for towing scenarios. High test chains are known for their increased tensile strength, making them ideal for heavy-duty towing applications.

Therefore, proof coil chain falls short in meeting performance and safety requirements for effective towing, which is why it is not recommended in such situations.