What type of knot is used to secure two lengths of rope of unequal diameters?

The becket bend is specifically designed to securely join two ropes of unequal diameters. This knot is advantageous because it maintains strength and stability even when the ropes differ in size, making it ideal for situations encountered in fire rescue operations or other emergency scenarios where equipment variability is common. The becket bend provides a reliable connection while allowing for easy adjustments and elimination of slippage, which is crucial when dealing with life-saving scenarios.

While the other knots mentioned have their uses, they are not as effective for this particular task. The bowline knot creates a fixed loop and is great for securing ropes, but it doesn't effectively join two dissimilar diameters. The clove hitch is useful for securing a rope to a post or similar fixture but does not serve the purpose of connecting two lengths of rope. The figure eight knot is primarily used as a stopper knot or to form a loop but is not designed to join two ropes effectively, especially if they vary in diameter. Thus, the becket bend stands out as the best choice for this specific application.