What knot is specifically used to join ropes of unequal diameters?

The becket or sheet bend is specifically designed for joining ropes of unequal diameters. This knot features a distinctive structure that allows it to securely attach two ropes together, even when one rope is much thicker or thinner than the other. The design of the knot ensures that the thinner rope is tucked effectively into the thicker rope, providing a strong and reliable hold. This is especially important in fire service operations where different types of rope may be utilized, and the capability to join them securely is crucial for safety and effectiveness during rescues or when handling equipment.

In contrast, the figure eight is primarily used for forming a loop at the end of a rope; it is not particularly suited for connecting two ropes of varying sizes. The bowline creates a fixed loop in a single rope, which also does not facilitate the joining of two differing diameters. Lastly, the overhand knot is primarily used for securing a rope and can easily slip or become loose, making it ineffective for securely joining unequal ropes. Therefore, the becket or sheet bend is the appropriate choice due to its unique design tailored for this specific task.