What knot is used to join two ropes of different diameters?

The becket bend is specifically designed to effectively join two ropes of different diameters, making it the best choice in this scenario. This knot features a secure and reliable structure that accommodates variations in rope size, ensuring a stable connection without slipping. The becket bend is commonly used in maritime applications as well as in firefighting and rescue contexts where the need to connect ropes of differing widths arises.

While other knots like the figure-eight and bowline are valuable for various applications, they are not typically utilized for joining dissimilar rope sizes and may not provide the same level of security as the becket bend. A sewing knot, primarily used in textile applications, does not apply here since it is not suited for securing ropes together. Therefore, the becket bend stands out as the appropriate knot for this purpose due to its design and functional effectiveness.