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The height by which a tooth of a gear projects beyond (outside for external, or inside for internal) the standard pitch circle or pitch line; also, the radial distance between the pitch diameter and the outside diameter



In a bevel gear, is the angle between elements of the face cone and pitch cone

Addendum angle


Coincides with the tops of the teeth of a gear and is concentric with the standard (reference) pitch circle and radially distant from it by the amount of the addendum. For external gears, the addendum circle lies on the outside cylinder while on internal gears the addendum circle lies on the internal cylinder

Addendum circle


In a bevel gear or hypoid gear, is the distance in the direction of the axis from the apex of the pitch cone to a locating surface at the back of the blank

Apex to back


Of a bevel gear is the angle between an element of the back cone and a plane of rotation, and usually is equal to the pitch angle

Back Angle


Of a bevel or hypoid gear is an imaginary cone tangent to the outer ends of the teeth, with its elements perpendicular to those of the pitch cone. The surface of the gear blank at the outer ends of the teeth is customarily formed to such a back cone

Back Cone


In a bevel gear is the distance along an element of the back cone from its apex to the pitch cone

Back cone distance


The striking back of connected wheels in a piece of mechanism when pressure is applied. Another source defines it as the maximum distance through which one part of something can be moved without moving a connected part



Reasons for requiring backlash include

Allowing for lubrication, manufacturing errors, deflection under load and thermal expansion


Of an involute gear is the circle from which involute tooth profiles are derived

Base Circle


Corresponds to the base circle, and is the cylinder from which involute tooth surfaces are developed

Base cylinder


Of an involute gear is the diameter of the base circle

Base Diameter


Used to refer to the larger of two spur gears that are in engagement in any machine

Bull gear


Is the shortest distance between non-intersecting axes. It is measured along the mutual perpendicular to the axes, called the line of centers. It applies to spur gears, parallel axis or crossed axis helical gears, and worm gearing

Center distance