Spur gears, the most common gear type, have a circular or cylindrical shape with teeth bordering the outer perimeter and are used for transmitting rotational torque and motion between parallel rotating shafts. A spur gear's pressure angle (PA), diametral pitch (also called DP or pitch), and its material are important factors to consider when purchasing. Gears come in several types for use in different power transmission configurations and for different applications, including bevel and miter gears (for rotating shafts perpendicular to each other), change gears (to increase or decrease torque and speed), helical gears (for high rates of rotational speed), internal gears (where one gear is nested inside the other), rack and pinion gears (for turning rotational motion into linear motion), and worm gears (for perpendicular shafts in tight spaces and quiet operation). Gears are suitable for use in the agriculture, automotive, construction, mining, and packaging industries, and can be found in a variety of machines, including bicycles, automobiles, and elevators, among others.
Boston Gear manufactures gears, gear drives, bearings, valves, shaft collars, couplings, and other power and fluid transmission components. The company, founded in 1877, is headquartered in Charlotte, NC, and meets International Organization for Standardization (ISO) standard 9001:2008 standard.