These are the simple and the most common kind of gears. These are generally in the form of cylinders or disks. The teeth of the gear are projected radially and the straight cut gears and the teeth are aligned parallel to axis of rotation.

The edges of the teeth are not parallel to the axis of rotation and are set at a certain angle. The gear is curved and therefore the angled teeth form a segment similar to helix.

This kind of reduction gear is a worm kind of construction. In this the helical gear is hardened and ground to close tolerances.

These are basically conical shaped and does not extend all the way to the vertex. In addition to two bevel gears in mesh, the vertices of the cones lie at a single point and the shaft too intersects the same point.