Gear: The larger of two meshed gears. If both gears are the same size, they are both called “gears”.
Pinion: The smaller of two meshed gears.
Face: The working surface of a gear tooth, located between the pitch diameter and the top of the tooth.
Flank: The working surface of a gear tooth, located between the pitch diameter and the bottom of the teeth
Addendum: The radial distance between the Pitch Circle and the top of the teeth.
Dedendum: The radial distance between the bottoms of the tooth and the pitch circle.
Module: Millimeter of Pitch circle Diameter to Teeth.
Backlash: Play between mating teeth.
Base Circle: The circle from which is generated the involute curve upon which the tooth profile is based.
Center Distance: The distance between centers of two meshing gears.
Circular Pitch: Distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth.
Tooth Thickness: The thickness of the tooth measured along an arc following the Pitch Circle
Clearance: The distance between the clearance circle and Dedendum circle.
Diametral Pitch: It is the ratio of number of teeth to the pitch circle diameter in millimeter.
Face Width: The width of the tooth measured parallel to the gear axis.
Top land: The top surface of the tooth.
Line of Action: That line along which the point of contact between gear teeth travels, between the first point of contact and the last.
Pitch Circle: The circle, the radius of which is equal to the distance from the center of the gear to the pitch point.
Pitch Point: The point of tangency of the pitch circles of two meshing gears, where the Line of Centers crosses the pitch circles.
Pressure Angle: Angle between the Line of Action and a line perpendicular to the Line of Centers.
Root Circle: The circle that passes through the bottom of the tooth spaces.
Root Diameter: The diameter of the Root Circle.
Working Depth: The depth to which a tooth extends into the space between teeth on the mating gear.