Which knot is used to connect two lines of the same diameter?

The square knot is the appropriate choice for connecting two lines of the same diameter. This knot is particularly effective for securing two ends of rope together in a simple and reliable manner. It consists of two overhand knots tied in opposite directions, which results in a flat, easy-to-untie structure that can hold firmly when equal tension is applied to both ends.

Using this knot allows for a straightforward connection that is easy to adjust or release when the need arises. Its design is particularly suited for lines of the same thickness because it can bind them together securely without slipping.

In contrast, while the other knots listed have their own specific uses, they do not serve as effectively for the purpose of connecting two lines of the same diameter. The bowline forms a fixed loop at the end of a line, making it suitable for different applications but not for directly connecting two pieces of rope. The sheet bend is designed to join two lines of differing diameters, thereby making it less suitable when the two ropes are the same size. The rolling hitch is primarily used to secure a rope to a cylindrical object, which does not pertain to simply connecting two lines.