What type of splice is used to connect two lines without significantly increasing the diameter?

The long splice is the correct choice because it is specifically designed to join two lines together while maintaining the line's overall diameter as much as possible. This makes it particularly useful in situations where the lines need to pass through hardware or fit within confined spaces without creating a noticeable bump or bulk at the connection point. The long splice integrates the two lines by interweaving their strands, thereby achieving a smooth transition between the two lines.

In contrast, a short splice typically increases the diameter at the splice point since it involves a more abrupt connection with the ends of the lines being joined. The French bowline, while useful for forming a loop at the end of a line, does not serve the purpose of connecting two lines together. The Carrick bend is excellent for joining two ropes of different sizes but also results in an increased diameter at the splice. Thus, the long splice offers the specific benefit of a streamlined connection, making it the appropriate choice for this scenario.