Hinge pin door stops are used in lieu of spring door stops when baseboards are absent, or when decorative baseboards make the latter a poor choice. They are designed to slip over the bottom hinge pin of the door, with one leg that points toward the door and the other toward the wall. They prevent the door — or door knob — from hitting the wall when the door is opened.
A spring door stop is a rigid rubber-tipped "finger" or spring, usually 3" (7.6 cm) in length. At the back is a round base with protruding wood screw. These are mounted about 2 feet (61 cm) in from the hinged side of the door, by pushing the end-screw against the baseboard, applying pressure, and simply turning until the base becomes flush. A door stop prevents an open door from swinging so wide as to allow the doorknob to damage the wall.
Hinge pin door stops are designed to slip over the existing bottom hinge pin of the door itself. Though there are a few basic designs, all have two rubber-tipped "legs." One leg is curved back on the door itself to keep the door stop from freely rotating on the pin, while the other leg is threaded through a retaining barrel, making it adjustable in length. It points in the opposite direction towards the wall so that when the door is opened, this leg will eventually contact the wall, preventing the door from swinging further.
Although traditional spring door stops are visible on baseboards, they are mounted so low and are so common that most people look right past them. Hinge pin ones are somewhat more visible as they are mounted on the door itself, and sit a little higher than a traditional door stop. For this reason they are available in many finishes and designs to accent any decor, or conversely, to be as inconspicuous as possible. They can be found in antique finishes of gold, bronze, or nickel, or polished finishes of brass, chrome or satin nickel. There are also heavy duty door stops for industrial use.
