Offset Pivot A special hanging device for heavy-duty doors, used on doors swinging one way only.

Olive Knuckle Hinge See Hinge.

Opening Size The size of a door frame opening, measured horizontally between jamb rebates and vertically between the head rebate and the finished floor. The opening size is usually the nominal size and is equal to the actual door size plus clearances.

Organic Coating A coating such as paint, lacquer, enamel or film in which the principal ingredients are derived from animal or vegetable matter or from some compound of carbon.

Overhang The horizontal distance that a roof projects beyond awafl.

Oxidation The reaction of substances with oxygen (air). This characteristic is both beneficial and detrimental in Architectural Hardware. Rust and corrosion are detrimental, destructive forms of oxidation. On the other hand, a finish that darkens with use, i.e., oxidised bronze or copper’s "patina" are examples of attractive, essentially non-destructive forms of oxidation.