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Metric Gears

Metric gears are defined by the module system, as follows:

Module
The length in mm of the pitch circle diameter per tooth.

MOD = PCD / N


Number of Teeth
The number of teeth on the gear.

N = PCD / MOD


Pitch Circle Diameter
The diameter of the pitch circle.

PCD = N x MOD


Outside Diameter
The outside diameter of the gear.

OD = (N + 2) x MOD


Center Distance
The distance between the axes of two gears in mesh.

C = PCD(g) + PCD(p)
                      2


Circular Pitch
The distance between adjacent teeth measured along the arc at the pitch circle diameter.

CP = pi x MOD


Circular Tooth Thickness
The width of a tooth measured along the arc at the pitch circle diameter.

CTT = CP / 2


Addendum
The height of the tooth above the pitch circle diameter.

A = MOD


Dedendum
The depth of the tooth below the pitch circle diameter.

D = H - A


Whole Depth
The total depth of the space between adjacent teeth.

Finer than 1.25 MOD:
H = 2.4 x MOD

1.25 MOD and coarser:
H = 2.25 x MOD