gear

1. addendum : the radial distance from the pitch circle to the outside diameter
2. dedendum : the radial distance between the pitch circle and the root diameter
3. circular thickness : the distance of the arc along the pitch circle from one side of a gear tooth to the other
4. circular pitch : the length of the arc of the pitch circle from one point on a tooth to the same point on the adjacent tooth
5. pitch diameter : the diameter of the pitch circle
6. outside diameter : the major diameter of the gear
7. root diameter : the diameter of the root circle measured from the bottom of the tooth spaces
8. chordal addendum : the distance from the top of the tooth to the chord connecting the circular thickness arc
9. chordal thickness : the thickness of a tooth on a straight line or chord on the pitch circle
10. whole depth : the total depth of a tooth space equal to the sum of the addendum and dedendum.
11. working depth : the depth of engagement of two mating gears
12. clearance : the amount by which the tooth space is cut deeper than the working depth
13. backlash : the amount by which the width of a tooth space exceeds the thickness of the engaging tooth on the pitch circles
14. diametral pitch : the number of gear teeth to each inch of pitch diameter
15. pressure angle : the angle between a tooth profile and a radial line at the pitch circle
16. center distance : the distance between the centers of the pitch circles

2.Gear Tooth Terminology
The following definitions apply to the three drawings shown below.

1. Heel and Toe identify the ends of the gear tooth. Imagine you and 12 other people are standing in a circle facing each other, your toes are pointing inside of the circle and your heels are pointing outside of the circle.
   • The Toe end of a ring gear is on the inside diameter of the gear.
   • The Heel end of a ring gear is on the outside diameter of the gear.
2. The Pitch Line is an imaginary line that divides the upper and lower halves of the gear tooth contact area.
3. The Pitch Point is the theoretical point where the pitch lines of both meshing gear teeth meet while rotating relative to one another.
4. The Root Line is an imaginary line that indicates the bottom of the meshing gear tooth contact area.
5. Face and Flank identify the area in the contact area of the gear tooth.
   • The Face of a gear tooth is the upper half of the gear tooth contact area.
   • The Flank of a gear tooth is the lower half of the gear tooth contact area.
6. The Drive Side and Coast Side of the gear tooth identify the sides of the gear tooth used under acceleration and deceleration.
   • The Drive Side is the convex side of the gear tooth and is used during acceleration and steady speed driving.
   • The Coast Side is the concave side of the gear tooth and is used during deceleration.
7. Backlash is the endplay between the gear teeth as the gear sets rotate relative to one another.
8. Clearance is the distance between the top of one gear tooth and the bottom of the area between two gear teeth it is meshing with.
9. Undercut is the bottom of the area between two gear teeth where no gear-to gear contact should be made.