Gears are identified by many types and there are many specific technical words to describe their definition. The most common way to classify gears is by category type and by the orientation of axes.
Gears are classified into 3 categories: parallel axes gears, intersecting axes gears, and nonparallel and nonintersecting axes gears.
Spur gears and helical gears are parallel axes gears. Bevel gears are intersecting axes gears. Screw or crossed helical, worm gear and hypoid gears belong to the third category. Table 1.1 lists the gear types by axes orientation.
(1) Parallel Axes Gears
(1.1) Spur Gear
This is a cylindrical shaped gear, in which the teeth are parallel to the axis. It is the most commonly used gear with a wide range of applications and is the easiest to manufacture.