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determined variously in the transverse, normal, or axial planes, and either in the direction of the pit  circles or on the line-of-action. Such measurements should be corrected to corresponding values a transverse pitch circles for general comparisons. (Figure 1.9)

CENTER DISTANCE (C), Distance between axes of rotation of mating spur or helical gears.

CHORDAL ADDENDUM (a_c) is the height from the top of the tooth to the chord subtending the circular-thickness arc. (Figure 1.10)

CHORDAL THICKNESS (t_c) is the length of the chord subtending a circular-thickness arc. (Figure 1.10)

CIRCULAR PITCH (p_c) is the distance along the pitch circle or pitch line between corresponding profiles of adjacent teeth. (Figure 1.1)

CIRCULAR THICKNESS (t) is the length of arc between the two sides of a gear tooth on the p4 circle, unless otherwise specified. (Figure 1.10)

CLEARANCE-OPERATING (c) is the amount by which the dedendum in a given gear exceeds addendum of its mating gear. (Figure 1.1)

CONTACT RATIO (Spur) is the ratio of the length-of-action to the base pitch.

CONTACT RATIO (Helical) is the contact ratio in the plane of rotation plus a contact portion a tributted to the axial advance.

DEDENDUM (b) is the depth of a tooth space below the pitch line; also, the radial distance beta, the pitch circle and the root circle. (Figure 1.1); dedendum can be defined as either nominal or operating.

DIAMETRAL PITCH (P_d) is the ratio of the number of teeth to the number of inches in the pitch diameter. There is a fixed relation between diametral pitch (P_d) and circular pitch (p_c): p_c = p / P_d

FACE WIDTH (F) is the length of the teeth in an axial plane.

FILLET RADIUS (r,) is the radius of the fillet curve at the base of the gear tooth. In generated this radius is an approximate radius of curvature. (Figure 1.13)

FULL DEPTH TEETH are those in which the working depth equals      2000"            
                                                                                            diametral pitch

GENERATING RACK is a rack outline used to indicate tooth details and dimensions for the design of a hob to produce gears of a basic rack system.

HELIX ANGLE (y) is the angle between any helix and an element of its cylinder. In helical gears a worms, it is at the pitch diameter unless otherwise specified. (Figure 1.7)

INVOLUTE TEETH of spur gears, helical gears, and worms are those in which the active portion of the profile in the transverse plane is the involute of a circle.

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