The Hyperlogos

A drain plug is a plug which seals a drain partially or completely, usually held in place by friction or by virtue of threads.

The most commonly found type of drain plug is those used in sinks, known as a stopper. The simplest form is generally made of rubber (or a flexible plastic, or silicone) and is simply molded in shape.

When we discuss the drain plug in an automobile, we're usually talking about the ones that are used for draining oil, transmission fluid, or differential fluid. These are almost always made of metal and they typically have either hex wrench flats on their top, square wrench flats on their top, or a 3/8" or 1/2" square inset on them which can be turned using a socket wrench (perhaps with an extension) without a socket, or driven with a square drive adapter. This type may also feature an embedded magnet (see picture, above) which captures ferrous metal shavings from the oil and can help extend the longevity of your engine, transmission, etc. Of course, the magnet cannot pick up the aluminum shavings from modern alloy parts.

Another type of automotive drain plug is that typically found in the automobile's body. These typically have a small hole in them to allow moisture to drain out the bottom, but not allow water to splash up through them, nor any significant moisture to be taken in due to ambient humidity. They are most commonly found in the rear of a car near the quarter panels, as the area between the rear of the quarter panel and the wheel house is typically sealed. Over time that area tends to fill up with dirt and assorted trash which must be cleaned out manually or it will clog the drain plug, potentially leading to interior rust and a general sogginess of your vehicle.

The final type of drain plug commonly located on automobiles is the type which is often used to seal older radiators. It's a butterfly-shaped bolt, sort of like a wing bolt (as opposed to a wing nut) that has a hole in it. When it is backed out sufficiently, it exposes a drain hole, and water flows out from the center of the bolt. Newer radiators usually just have a plastic plug that is removed completely. Sometimes there is a plastic plug which can be removed entirely for full flow, but which can also be backed out slightly to allow fluid to flow through a drain port and/or hose directly beneath the plug.