being at either the very top or very bottom of the differential crown wheel. In the 1910s, they were common on trucks; to gain the most clearance on muddy roads, the worm was placed on top. In the 1920s, the Stutz firm used them on its cars; to have a lower floor than its competitors, the worm was located on the bottom. An example circa 1960 was the Peugeot 404. The worm drive protects the vehicle against rollback. This ability has largely fallen from favour, due to the higher-than-necessary reduction ratios. A more recent exception to this is the Torsen differential, which uses worm wheels and planetary worms, in place of the bevel gearing of conventional open differentials. Torsen differentials are most prominently featured in the Humvee and some commercial Hummer vehicles, and as a centre differential in some all-wheel drive systems, such as Audi's quattro. Very heavy trucks, such as those used to carry aggregates, often use a worm drive differential for strength. The worm drive is not as efficient as a hypoid gear, and such trucks invariably have a very large differential housing, with a correspondingly large volume of gear oil, to absorb and dissipate the heat created. Worm drives are used as the tuning mechanism for many musical instruments, including guitars, double basses, mandolins, bouzoukis, and many banjos (although most high-end banjos use planetary gears or friction pegs). A worm drive tuning device is called a machine head. Plastic worm drives are often used on small battery-operated electric motors, to provide an output with a lower angular velocity (fewer revolutions per minute) than that of the motor, which operates best at a fairly high speed. This motor-worm-drive system is often used in toys and other small electrical devices. A worm drive is used on jubilee-type hose clamps or jubilee clamps. The tightening screw's worm thread engages with the slots on the clamp band. Occasionally a worm drive is designed to run in reverse, resulting in the worm shaft turning much faster than the input. Examples of this may be seen in some hand-cranked centrifuges, blacksmithing forge blower, or the wind governor in a musical box. Left-hand and right-hand worm A right-hand helical gear or right-hand worm is one in which the teeth twist clockwise as they recede from an observer looking along the axis. The designations, right-hand and left-hand, are the same as in the long-established practice