π / Pd (Φ = Pressure Angle, Pd = Diametral Pitch).Base Pitch (Pb) – is the circular pitch in the plane of rotation at the base circle.

Base Helix Angle (Ψb) – is the helix angle at the base cylinder.

Cos Φ (D = Pitch Diameter, Φ = Pressure Angle.

Base Diameter (Db) – is the diameter of the circle from which the involute form is generated.Base Lead Angle (λb) – is the lead angle at the base cylinder.Base Cylinder – is the cylinder of the same diameter as the base circle.Base Circular Thickness (tb) – is the length of arc on the base circle between two involute curves forming the profiles of a tooth.Backlash Variation – is the difference between the maximum and minimum backlash occurring in one revolution of the larger of a pair of mating gears.Backlash (B) – is the amount by which the width of a tooth space exceeds the thickness of the engaging tooth on the pitch circles.Axial Runout – is the runout measured in a direction parallel to the axes of rotation.Axial Pressure Angle (Φx) – is the angle between the tangent to the tooth profile in an axial plane at the pitch surface and a line perpendicular to the axis.Px = Pt / Tan Ψ (Pt = Transverse Circular Pitch, Ψ = Helix Angle) Axial Pitch (Px) – is the distance in an axial plane surface between corresponding adjacent tooth profiles.Axial Direction – A direction parallel to an axes.Arc of Recession (Qr) – is the arc of pitch circle through which a tooth travels from the time it is in contact with a mating tooth at the pitch point until contact ceases.Arc of Approach (Qt) – is the arc of the pitch circle through which a tooth travels from the time it first makes contact with a mating tooth until it is in contact at the pitch point.Angular Pitch (θN) – is the angle subtended by the circular pitch.Angular Bevel Gears – are bevel gears in which the axes are not at a right angle.Spur Gears - a = 1 / Pd (Pd = Diametral Pitch) Helical Gears - a = 1 / Pnd (Pnd = Normal Diametral Pitch) Addendum (a) – is the radial or perpendicular distance between the pitch circle and the top of the teeth.Active Profile – is that part a gear tooth that actually comes into contact with its mating tooth along the line of action.Related Resources: gears Gear Terminology and Equations

The circle of gear order of the stick