Prevent line twist with these affordable Barrel Swivels. Swivel color Black. A fishing swivel is a small device consisting of two rings connected to a pivoting joint. The line from a rod and reel is tied to one end, and a length of fishing line, often terminated by a hook, lure or sinker, is tied to the other. The main purpose of the swivel is to allow the line to untwist during line retrieval, preventing undesirable tangling. This is particularly important for users of monofilament test line. A secondary benefit of the fishing swivel is that it may stop a sliding sinker, which depending on fishing method may be placed before or after the swivel.