Spiral Bevel Gears:
While the teeth of a bevel gear are inclined at an angle to the face of the bevel, these gears are called as helical bevel gears or spiral bevel gears. A gear of this kind is illustrated in Figure (a). They run quitter in action and remain point contact. If spiral bevel gear contain curved teeth but along zero degree spiral angle, it is called as zerol bevel gear.
(a) Spiral Bevel Gear (b) Zerol Bevel Gear