Oblique drawing: Oblique drawing is the least natural method of drawing a 3D object. The object is shown with one surface parallel to the viewing plane, and depth is represented by lines drawn at a 45° angle.

Off-cut: Off-cut is the term used to describe the unused portion of material from which an object has been cut.

Off set: Off set refers to surfaces slightly angled to allow for distortion when welding.

Opposite side: The opposite side in a right angled triangle is the side opposite a given angle which is not the hypotenuse.

Orientation view: Orientation view is the layout which shows adjacent views of an object.

Orthogonal: Orthogonal means relating to, or composed of right angles. Orthogonal drawings are 2D drawings of 3D objects created by orthographic projection.

Orthogonal drawings: Orthogonal drawings are 2D drawings of 3D objects created by orthographic projection.

Orthogonal projection: In geometry, an orthogonal projection of a 3D object onto a plane is achieved by a series of intersecting lines drawn through all points of the object, orthogonally (at right angles) to the plane of projection.

Orthographic projection: Orthographic projection shows the object as it looks from the front, right, left, top, bottom, or back, and these views are typically positioned relative to each other.

It uses multiple views of a 3D object in a 2D drawing, taken from points of view rotated about the object's center through increments of 90°.

Over press: An over press is a fault in the pressing of a transitional shape where too much pressing of the transition has occurred due to the press being set incorrectly.

Over-roll: Over-roll is the term used to describe a cylinder which is rolled past the required diameter.

Oxy acetylene set: An oxyacetylene set is made up of two bottles of gas (oxygen and acetylene) and the cutting attachment. When the two gasses are combined a high temperature is created. The chemical reaction between the two gasses and the steel (which is called the ignition point) is used to cut mild steel. This is only possible with ferrous metals.

Oxy cutting: Oxy cutting is the process by which steel is cut using the chemical reaction between two gasses, oxygen and acetylene. This reaction only happens with ferrous metals.