Sprockets and gears are both used to transmit power within machines, or to move items by interlocking with them. Though a sprocket and a gear may seem similar, there are a number of differences between the two. The main functional difference between a sprocket and a gear is that a gear is a toothed wheel designed to mesh with other gears and transmit movement to them, while a sprocket is a toothed wheel designed to engage and move a flexible indented or perforated item, such as a bicycle chain or a strip of film. Due to this design difference, their applications are also different. Gears tend to be more flexible in terms of how they can be applied than sprockets.

A significant difference between a sprocket and a gear is that sprockets’ function limits their design — their teeth must be constructed to fit into the perforations or slots of the items they are designed to move. The possibilities for design variations are limited. Gears, on the other hand, mesh directly with each other, and thus lend themselves to a wide variety of designs. For instance, a gear’s teeth might be on the outside of the wheel, or on the inside circumference; another type, called a worm gear, isn’t a wheel at all, but a threaded rod. This wide variety of design possibilities makes gears more versatile than sprockets.

Another important difference between a sprocket and a gear is the impact of their being damaged on the machine they serve. The two sprockets that carry a bicycle chain, for example, also guide the chain in a straight line, and if a single tooth on one of the sprockets breaks, the chance of the chain’s being thrown off, incapacitating the bicycle, increases. If a tooth breaks off a gear, on the other hand, assuming the broken tooth falls out of the machine’s works, there’s little likelihood that the machine itself will fail as a result, although it may experience reduced efficiency.

Gears are found in many machines. They're an integral component of automobile engines, for example, transmitting power from the engine to the drive wheels. Precision made gears also operate many clocks and watches. Some gear arrangements, like worm drives, can limit the transmission of power to a single direction without any additional devices like brakes.

The most commonly known examples of sprockets are on bicycles, tracked vehicles like tanks and bulldozers, film cameras, and film projectors. In each case, rotation of the sprocket moves a flexible device like a bicycle chain or strip of photographic film. In those cases where the flexible device is a continual loop, as in bicycles and tracked vehicles, the many segments that make up the loop make it more vulnerable to wear and tear, necessitating more maintenance.

The differences between a sprocket and a gear, and the gear’s general superiority over the sprocket, usually lead designers to choose gears when they can. A famous example is cars and trucks with rear-wheel drives, which employ a rigid drive shaft to transmit power from the engine to the drive wheels. Bicycle-type chain drives were popular with automotive vehicles, but their popularity waned, and the last chain-driven car was manufactured in the 1960s.