Swivel

A swivel is a connection that allows the connected object, such as a gun, chair, swivel caster, or an anchor rode to rotate horizontally or vertically.
Swivel designs.
A common design for a swivel is a cylindrical rod that can turn freely within a support structure. The rod is usually prevented from slipping out by a nut, washer or thickening of the rod. The device can be attached to the ends of the rod or the center. Another common design is a sphere that is able to rotate within a support structure. The device is attached to the sphere. A third design is a hollow cylindrical rod that has a rod that is slightly smaller than its inside diameter inside of it. They are prevented from coming apart by flanges. The device may be attached to either end.
A swivel joint for a pipe is often a threaded connection in between which at least one of the pipes is curved, often at an angle of 45 or 90 degrees. The connection is tightened enough to be water- or air-tight and then tightened further so that it is in the correct position.
Anchor rode swivel.
Swivels are also used in the nautical sector as an element of the anchor rode and in a boat mooring systems. With yachts, the swivel is most commonly used between the anchor and chain. There is a school of thought that anchor swivels should not be connected to the anchor itself, but should be somewhere in the chain rode.
The anchor swivel is expected to fulfill two purposes:
Swivel the concerns.
The biggest concern about anchor swivels is that they might introduce a weak link to the rode.