Which two types of stoppers are commonly used in nautical applications?

In nautical applications, the two types of stoppers most commonly used are indeed related to specific knot techniques. The correct pair focuses on knots that are effective for securing lines, preventing them from slipping or coming undone under load.

The Criss Cross knot, often used to create a stopper knot, provides a strong grip and is excellent for mooring or securing lines where a reliable hold is needed. The Rat Tail knot, however, is useful for various applications due to its ease of use and ability to tighten under tension, ideal for managing line ends.

In contrast, the other choices include knots that have different primary purposes. For instance, the Figure Eight and Bowline are primarily used for forming loops or securing items, not specifically as stoppers. Similarly, the Clove Hitch and Square Knot are useful for securing lines to objects or tying two ends of rope together, but they do not serve the specific function of being stoppers. Lastly, the Double Fisherman and Half Hitch are also effective knots but are not traditionally categorized as stoppers in the same context as the Criss Cross and Rat Tail.