Protractors and angle gages measure the angle between two surfaces of a part or assembly

Squares are used to indicate, by visual comparison, whether two surfaces are perpendicular.

Bevel and miter gears have conical faces that operate on intersecting axes.

Hypoid gears have specially formed teeth on a circular face that are driven by a worm-like drive on non-intersecting axes.

Gears are mechanical devices that transmit power and motion between axes.

Gearboxes and gearheads are speed reducers that consist of a set of gears, shafts, and bearings in an enclosed housing.

Metric gears are defined by module, which designates the center-to-center distance between successive teeth.