Gudgeons are simple fittings, usually circular, that are applied to some sort of surface. Normally, a gudgeon is composed of metal, and makes it possible for some other fixture to be attached to the device while still allowing some range of motion. This allows the circular fitting to perform much of the same function as a bearing, although the device is used in situations where a bearing would not work.
The most common application of a gudgeon is found on a sailboat. Along with a pintle, the fitting is employed to make it possible for a boat rudder to pivot with relative ease, making the steering of the vessel much easier. In many designs, the pintle, which is simply a pin that is inserted into the hole of the gudgeon, establishes the connection between the body of the boat while still allowing the rudder to move as needed.
A circular fitting that is used on some type of seagoing vessel may be referred to as a rudder gudgeon or a transom gudgeon. Determining which designation is used depends on where the fitting is actually affixed, the rudder or the body of the boat known as the transom. Both names are descriptive of where the device is affixed to the boat structure, and provide some idea of the function. Most designs call for the use of more than one gudgeon and pintle on a given rudder. Generally, there is some type of weight applied to one end of the pintle that prevents it from slipping out of the fitting once it is in position.
The gudgeon can also be used in other applications. One has to do with water wheels on paddleboats. Here, the function is very similar to that of a rudder gudgeon, in that pins are used to keep the wheel in proper alignment, while not inhibiting the free movement of the wheel as water cascades over the wheel. The circular fitting design of the device makes it relatively easy to fix in place, and also to replace when and as needed.
While the gudgeon is normally constructed using some type of metal that holds up well to a lot of wear, the device can also be constructed with forms of hard plastic. Circular fittings of this type are not used in situations such as securing rudders to boats, or other situations where the wear is constant. Plastic fittings like this are more likely to be used in devices that see less wear, such as a pivoting device for wind chimes, which allows the chimes to turn whenever a brisk wind comes along.