What knot is commonly used for tying lines of the same size together?

The square knot, also known as the reef knot, is widely recognized for its effectiveness in tying ropes of the same diameter together. This knot is particularly valued for its simplicity and reliability; it holds securely under tension yet is easy to untie when the need arises.

When two lines of similar size are joined, the square knot maintains a flat profile, which is advantageous for preventing slipping. Its design allows it to tighten when pulled, ensuring a secure connection for various applications, such as securing sails or bundling materials. While other knots serve different purposes, such as the figure eight for creating a loop or the bowline bite for forming a fixed loop, none match the square knot's specific utility for joining two equal-size lines.

Thus, the square knot is the most appropriate choice in scenarios that require the reliable joining of two lines of the same size.