The standard center distance C{a} is dependent upon ratio, tooth pitch, and pressure angle. Standard Center Distance:

A pair of gears may operate on modified or standard center distance. The standard center distance is given by:

For gears that operate on standard centers:

C = C_{STD}

Modified Center Distance:

For gears that operate on modified centers, the center distance modification is:

ΔC=C-C_{STD}

The value for the pitch diameter of the pinion is normally calculated and entered here. The value can be directly entered by checking the box by the side of the field.

The net contacting face width F{b} excludes any face width that is non-contacting because of chamfers or radii at the ends of the teeth. For double-helical gears the net face width equals the total face width minus the gap between the helices.

The normal diametral pitch is shown if US customary units are selected as a default (see 1.3.3). For metric units also the normal module can be shown instead.

The normal diametral pitch defines the size of a tooth. It is π divided by the
normal pitch P_{nd} = π∕p. So the tooth thickness increases with a decreasing
normal diametral pitch. The value can be directly entered by checking the box
by the side of the field. So you have the possibility to select a standard
value.

The normal module m_{n} is only shown if metric units are selected (see 1.3.3). For
US customary units you see the normal diametral pitch instead.

The normal diametral pitch defines the size of a tooth. It is the normal pitch
divided by π m_{n} = p∕π. So the tooth thickness increases with an increasing
module. The value can be directly entered by checking the box by the side of the
field. So you have the possibility to select a standard value (with are normally
given in millimeters).