The gears are classified as follows.
1. According to the position of axes of shafts.
(a) Shaft axes Parallel
Spur Gears
Helical Gears
Herringbone Gears
Rack and Pinion
(b) Shaft axes Intersecting
Straight Bevel Gears
Spiral Bevel Gears
(c) Shaft axes non-intersecting and non-parallel
Hypold Gears
Worm gears
Screw gears
2. According to the peripheral velocity of the gears
(a) Low-velocity gears
(b) Medium velocity gears
(c) High-velocity gears
3. According to the type of gears
(a) External gearing
(b) Internal gearing
(c) Rack and pinion
4. According to the position of teeth on the gear surface
(a) Straight gear
(b) Inclined gear
(c) Curved gear
