Which knot is used to tie two ropes of unequal size together?

The becket bend is specifically designed for joining two ropes of unequal sizes. This knot provides a strong connection that maintains a low profile, making it particularly useful in situations where one rope is thicker than the other. It creates a secure bond while allowing for the two different diameters to sit comfortably against each other.

In contrast, the square knot is effective primarily for tying two ends of the same type and size together, which can lead to slipping if the ropes differ significantly in size. The bowline creates a fixed loop at the end of a rope but does not serve the purpose of directly joining two ropes. The double fisherman's knot is used to securely join two ropes when both are of the same or nearly the same size but may not be as effective when there is a significant disparity in diameter. Therefore, the becket bend is the most appropriate choice for connecting ropes of differing sizes.