**Active profile**- Is that part of the gear tooth that actually comes into contact with its mating tooth along the line of action.

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

**Angular bevel gears**- Are bevel gears in which the axes are not at right angles.

**Axle**- A round, hollow metal bar on which the rear wheels are mounted on.

**Axial load bearing**- A bearing in which the load acts in the direction of the axis of rotation.

**Axial pitch**- Is the distance in an axial plane surface between corresponding adjacent tooth profiles.

**Axial pressure angle**- 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.

**Backlash**- A strong and sudden reverse movement in a moving part of a machine.

**Base circle**- An imaginary circle used in involut gearing to generate the involutes that form the tooth profiles.

**Base lead angle**- Is the lead angel between the base cylinder.

**Bevel gears**- Are gears of conical form designed to operate on intersecting axes.

**Center distance**- The distance between axes of two gears in mesh.

**Circular pitch**- Is the distance on the circumference of the pitch circle between the corresponding points of adjacent teeth.

**Circular thickness**- The thickness at the point where the gear engages.

**Clearence**- The difference between the dedendum of one gear and the addendum of the mating gear.

**Cogwheel**- A wheel with a rim notched into teeth, which meshes with those of another wheel or a rack to transmit or receive motion.

**Common tangent**- The line tangent to the pitch circle at the pitch point.

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

**Diametrical pitch**- The number of teeth per one inch of the pitch circle diameter.

**Differential gear**- A bevel gear that permits rotation of two shafts at different speeds.

**Double helical gear**- Is a gear of cylindrical form with two sections of teeth that engage simultaneously with teeth of similarly designed mating gear.

**External gear**- The simplest gear systems with cylindrical gears and teeth parallel to the axis.

**Face gear**- It is a gear with cogs mortised into its face, usually in conjugation with a lantern pinion.

**Face width**- Is the width of the pitch surface.

**Gears**- It is a toothed machine part that meshes with another toothed part to transmit motion or to change speed or direction.

**Gear center**- Iis the center of pitch circle.

**Gear box**- The manual transmission on a shifter kart.

**Gear ratio**- It is the ratio between number of teeth of the meshing gears.

**Gear train**- A gear train is two or more gear working together by meshing their teeth and turning each other in a system to generate power and speed.

**Helical gear**- Is a cylindrical gear with helical teeth.

**Idler gear**- A gear wheel placed between two other gears to transmit motion from one to the other.

**Involute**- Is the curve described by the end of a line that is unwound from the circumference of a circle.

**Internal gears**- Gears that have cylindrical pith surface with teeth parallel to the axis.

**Line of action**- Is that portion of the common tangent to the base circles along which contact between the mating involute teeth occurs.

**Line of contact**- Is the line or curve along which two tooth surfaces are tangent to each other.

**Miter gear**- Bevel gears put together with equal numbers of teeth and axes that are usually at right angles.

**Module**- Is the ratio of the pitch diameter to the number of teeth.

**Path of contact**- The path traced by the contact point of a pair of tooth profiles.

**Pawl**- A mechanical device allowing rotation in only one direction.

**Pinion**- A small cogwheel, the teeth of which fit into those of larger gearwheel or those of a rack.

**Pitch circle**- Is the circle through the pitch point having its center at the axis of the gear.

**Pitch diameter**- Is the diameter of the pitch circle.

**Pitch radius**- Is the radius of the pitch circle.

**Planetary gears**- A device allowing several gears to orbit about others.

**Pressure angle**- The angle between the tooth profile at the pitch circle diameter and a radial line passing through the same point.

**Rack gear**- It is a gear of infinite pitch radius into which a pinion meshes.

**Ratchet**- A toothed wheel or bar that catches and holds a pawl, which thus prevents backward movement.

**Spiral bevel gears**- Designed for an angle change of 90 degrees, where the two axes are concurrent and in the same plane.

**Sprockets**- Are teeth like projections arranged on a wheel rim to engage the links of a chain.

**Spur gear**- They connect parallel shafts, have involute teeth that are parallel to the shaft and can have internal or external teeth.

**Sun gear**- Small gearwheel that revolves around its own axis and also around a gear meshing with it.

**Velocity ratio**- The ratio of the number of revolutions of the driving gear to the number of revolutions of the driven gear, in a unit of time.

**Whole depth**- Is the radial distance between outside circle and the root circle.

**Working depth**- Is the greatest depth to which a tooth of one gear extends into the tooth gear of the mating gear.

**Worm gear**- It is a gea with one or more teeth in the form of screwed threads.

**Zerol bevel gears**- Is a bevel gear with intersecting shafts.