Mechanical Systems

Power Transmission Components 201

Power Transmission Components provides an overview of various components used to transmit energy through mechanical systems. Many systems use gear trains, belt drive systems, chain drives systems, or a combination of these to transfer energy from a power source to a point of use. Industrial applications requiring frequent stopping and starting and varying operational speeds use clutching mechanisms controlled by manual or automatic transmissions.

As certain power transmission components are best suited for certain applications, manufacturers must determine which components are most appropriate for a given situation. Understanding advantages and disadvantages of various components based on operating speeds, load capacity, and other factors helps ensure efficient operations. Professionals in manufacturing should understand the basics of power transmission in all its variations.

  • Difficulty Intermediate

  • Format Online

  • Number of Lessons 19

  • Language English


Or fill out this form and a specialist will contact you shortly

Course Outline
  • Power Transmission
  • Energy Conversion
  • Prime Movers
  • Common Types of Prime Movers
  • Gear Trains
  • Types of Gears
  • Review: Prime Movers, Gears, and Power Transmission
  • Belt Drives
  • Types of Belts
  • Chain Drives
  • Types of Chains
  • Bearings
  • Types of Bearings
  • Review: Belt Drives, Chain Drives, and Bearings
  • Couplings
  • Clutches
  • Transmissions
  • Types of Transmissions
  • Review: Bearings, Couplings, Clutches, and Transmissions
  • Describe power transmission.
  • Describe how energy is used in mechanical systems.
  • Describe the function of prime movers.
  • Distinguish between types of prime movers.
  • Describe the function of gear trains.
  • Distinguish between different types of gears.
  • Describe the function of belt drive systems.
  • Distinguish between different types of belts.
  • Describe the function of chain drive systems.
  • Distinguish between different types of chains.
  • Describe the function of bearings.
  • Distinguish between different types of bearings.
  • Describe couplings.
  • Distinguish between different types of clutches.
  • Describe transmissions.
  • Distinguish between manual and automatic transmissions.
Vocabulary Term


Positioned accurately in relation to one another. Two aligned shafts are parallel and form a perfectly straight line.

alignment tolerance

The limit of acceptable misalignment for a flexible coupling. Couplings connecting shafts beyond the alignment tolerance can quickly wear out.

American National Standards Institute

ANSI. A private, nonprofit organization that administers and coordinates voluntary standards and systems. American National Standards Institute ratings provide design standards for chain manufacturers.


The degree of space between two lines connected at a single point. Various angles are used in angular gear trains to maximize space and mechanical efficiency.

angular gear trains

A gear train composed of gears with intersecting shafts. Angular gear trains use a variety of gear designs.

antifriction bearing

A bearing with rolling parts inside that support the motion of a load. Antifriction bearings are also called rolling-element bearings.


A rotating component attached to the output shaft on an electromagnetic clutch. The armature is pulled against the rotor by magnetic force when the clutch is engaged.

automatic transmission

A complex transmission that does not require the operator to shift gears. Automatic transmissions often use a system of multiple gearboxes in order to change the speed and torque of mechanical energy.

axial load

Force that is applied parallel to the bearing's axis. Axial loads are also called thrust or linear loads.


An imaginary straight line passing through the center of an object. A round component such as a gear typically rotates around its axis.

ball bearing

A rolling-element bearing containing metal balls placed between two parts. A ball bearing allows machine parts to move with little friction.


A friction-reducing device that allows one moving part to glide past another moving part. Bearings operate using a sliding or rolling mechanism.

bearing surfaces

The area of contact between two objects. Bearing surfaces, such as those composing plain bearings, can simply be the surface of a cylindrical hole in which a shaft rotates.

belt drive system

A mechanical system consisting of a flexible belt and at least two fixed pulleys that is used to transmit motion. Belt drive systems are low maintenance and do not require lubrication.


A band of flexible material that is looped around two or more fixed pulleys to transmit motion. Belts are made of various materials and come in different types, such as flat belts, round belts, and V-belts.

bevel gear

A type of gear with cone-shaped teeth cut at an angle. Bevel gears are often used in angular gear trains.

block-and-pin U-joint

The most common type of U-joint. A block-and-pin U-joint has two open-ended shafts that are connected to a center block with pins.


A specific type of clutch that slows and stops power transmission. Brakes engage a rotating shaft and a fixed component to produce friction.

brake pad

A device, usually made of metal, on a friction brake that is lined with a friction material. A brake pad presses against a rotor during braking to resist motion.


The process of engaging components in a special clutch, or brake, to stop power transmission. Braking uses friction to slow or stop the transmission of power and torque.


A part found in some antifriction bearings that separates and prevents rolling elements, such as balls, from sliding against each other. The cage rotates within the inner and outer races.


A mechanical device attached to a friction disc brake that contains the rotor and brake pad. Calipers use a clamping motion to press the brake pad against the rotor, creating friction that resists motion.


Strong material made from tightly woven fabric such as cotton. Canvas belts are durable and are typically less expensive than rubber belts.


The section of the lathe that slides back and forth along the ways and supports the cross-slide and cutting tool. The carriage can move in two directions, usually by converting rotary motion to linear motion.

center block

The base of a U-joint to which shaft inserts are attached. The center block on a block-and-pin U-joint remains fixed while the shaft inserts pivot on joints.

chain drive system

A system consisting of a chain and sprockets that is used to transmit motion. Chain drives do not slip because sprocket teeth mesh with links in the chain.


A series of interlocking metal rings or connected metal links. Chains in mechanical systems mesh with teeth on sprockets to transfer energy.


A device that controls the transfer of power between machine components by engaging and disengaging two rotating shafts. Clutches are often used to quickly start and stop the transfer of power in industrial applications.


The process of engaging the components in a clutch to allow for power transmission. Clutching also allows for the transfer of torque from an input shaft to an output shaft.


Multiple loops of conducting wire used to create a magnetic field when current is passed through it. Coils are used in electromagnetic clutches.

compliant coupling

A type of flexible coupling that can absorb shock. Compliant couplings can help protect against excess wear.


A gradually tapering rounded shape. The teeth of some bevel gears are conical.


The presence of foreign materials, such as dirt, in a lubricant. Contamination in a lubricant can damage machinery.


The gradual chemical attack on a material by atmosphere, moisture, or other agents. Some chains are designed to resist corrosion.


A component that connects two shafts in a mechanical system in order to transfer motion. Different types of couplings can be used for various applications.


A machine for lifting and moving extremely heavy loads. Cranes can be driven manually or powered automatically.

double-pitch roller chain

A roller chain with links spaced twice as far apart as a standard roller chain. Double-pitch roller chains are less expensive but cannot operate as quietly or as fast as a standard chain.

drill press

A machining tool that penetrates the surface of a workpiece and makes a round hole. Drill presses can be used for a variety of holemaking operations.

drilling rigs

A large machine used to drill holes in the ground. Drilling rigs are often used to excavate building sites or dig wells for extracting subsurface minerals.

drive gear

The gear that receives energy from the power source via an input shaft. Drive gears transmit power to driven gears to perform work.

drive pulley

The fixed pulley in a belt drive system that receives energy from the power source. The driver pulley transfers energy to the driven pulley via the belt.

drive sprocket

The sprocket in a chain drive system that receives power from the power source. The driver sprocket transfers energy to the driven sprocket via the chain.

driven gear

The gear that receives motion from the drive gear on a machine. Driven gears often transmit power to another meshing gear or an output shaft to perform work.

driven pulley

The fixed pulley in a belt drive system that receives energy from the driver pulley via the belt. The driven pulley is often connected to a point of use where work is performed.

driven sprocket

The sprocket in a chain drive system that receives energy from the driver sprocket. The driven sprocket is often attached to an output device that performs work.

electric linear motor

A machine that converts electricity into mechanical energy or motion. Linear motors are sometimes called linear actuators.

electric motor

A machine that converts electricity into mechanical energy or motion. An electric motor is a common power source for a mechanical system.

electrical energy

The energy created by the movement of electrons. Electrical energy can be converted into light, heat, or motion.

electromagnetic clutch

A noncontact clutch that uses magnetic forces to transmit power between input and output shafts. Electromagnetic clutches are used in some automated machinery and provide quick response times.

electromagnetic forces

Energy from a magnetic field that is produced by an electric current. Electromagnetic forces are used to transfer energy and torque in an electromagnetic clutch.

electronic drills

A tool that drives screws and creates holes. Electronic drills use transmission components to alter the speed and rotational direction.


The ability or capacity to perform work. Energy, which is never created or destroyed, may be potential or kinetic and may appear as electrical, mechanical, thermal, or chemical energy.

external combustion engines

A type of engine in which fuel is burned outside the engine. External combustion engines include steam engines and Stirling engines.


A component's design specifications intended for specific functionality or enhanced capability. Different features of plain bearings provide different functional advantages.

fixed pulleys

A circular device that is used in belt drive systems to transmit motion. Fixed pulleys rotate around an axis that does not move.

fixed pulleys

A device consisting of a wheel rigidly fixed to a shaft that is used with a belt to transmit energy and motion to another fixed pulley. All belt drives contain at least two fixed pulleys.


A projecting rim or edge. Flanges on the input and output shafts of a positive clutch transfer energy through interlocking teeth.

flat belt

A belt consisting of a flat loop of material used to transmit motion between two pulleys. Flat belts can be made of various materials, such as rubber, canvas, plastic, or flexible metals.


The ability to bend or curve. Some couplings can flex in order to connect misaligned shafts.

flexible coupling

A type of coupling that can connect aligned shafts or flex to accommodate shafts that are slightly misaligned. Flexible couplings have a limited tolerance for misalignment.


An influence, such as a push or a pull, which produces a change in an object's motion or state of rest. Forces have specific directions and magnitudes.


A type of powered industrial truck that has two prongs on the front for lifting pallets of material. Forklifts are one of the most common types of PIT.


The resistance between the contact surfaces of two objects. Friction is required in a belt drive system to transmit motion.

friction clutch

The most common type of clutch used in mechanical systems. A friction clutch contains two discs, each connected to its own shaft, that can be forced together to transfer energy.

friction materials

A mixture of substances bonded to clutch discs or brake pads to reduce wear on clutching and braking components. Friction materials on a friction disc clutch are usually bonded to the disc on the input shaft.

gear shafts

A cylindrical bar used to support and rotate gears. Gear shafts connect gears to other components in order to transmit rotary motion through a mechanical system.

gear shift

A mechanism that allows the operator of a manual transmission to move the gears into various positions. Changing gear combinations alters the speed and torque of mechanical energy.

gear trains

A system of gears used to transmit rotary motion from one part of a mechanical system to another. Gear trains contain two or more meshing gears.


An enclosed system of assembled gears that transmits mechanical energy from a prime mover to an output device. A gearbox can also change the speed, direction, or torque of mechanical energy.


A round or cylindrical mechanical component with teeth that is used to transmit power. Gears are designed to mesh with one another and can alter the speed, torque, or direction of mechanical energy.


A commonly used semisolid industrial lubricant composed of oil and a chemical soap or other additive. Grease is often used in applications requiring heavy loads.

heat engine

A device that converts heat energy into mechanical or electrical energy. A heat engine is a type of prime mover.

helical gear

A type of gear with slanted teeth. Helical gears are quieter than spur gears, but they are more expensive and produce side loads.

helix angle

The angle between the axis of a helical gear and an imaginary line that is tangent to the gear tooth. Helix angles can vary in size from 0 to 90 degrees.


A protective cover designed to contain or support a mechanical component. Housings may be used to enclose gear drives.

idler gears

A gear that is used to keep the direction of motion consistent between a drive gear and a driven gear. Idler gears only influence direction and do not alter speed and torque between drive and driven gears.

input device

A power transmission component that receives mechanical energy from a prime mover. Input devices, such as input shafts, begin moving in response to receiving mechanical energy, which initiates power transmission.

input shaft

A rotating shaft that receives power from the power source. Input shafts introduce power into mechanical systems.

internal combustion engines

A type of engine in which fuel is burned inside the engine. Internal combustion engines include gas turbines and types of diesel motors.


The process of meeting, cutting across, or overlapping. Intersecting lines form the shape of an "X."

inverted-tooth chain

A type of chain with teeth on its links that mesh with teeth in the sprockets of a chain drive. An inverted-tooth chain, or silent chain, operates quietly and smoothly.


A machine tool commonly used to create cylindrical forms. A lathe holds a cylindrical workpiece on one or both ends while the cutting tool is gradually passed along the surface of the rotating part.


Fabric made from cowhide that offers resistance to heat and other hazards. Leather is used less commonly to make belts for belt drive systems today than in the past.

linear motion

Motion that takes place along a straight line. Linear motion in mechanical systems is often produced using power transmission components designed to convert rotary motion.

link plates

The flat surface on each side of a chain link joined together by the link pins. Link plates are used to form connected chain links.


A single unit of a chain usually fastened together by pins and clips. Individual chain links mesh with teeth in a sprocket.


The amount of force or pressure placed on a component or system. Belt drives can sustain a range of light or heavy loads.


A substance used to reduce friction between two surfaces in relative motion. Common lubricants used in industrial applications include oil and grease.


The application of a substance to reduce friction and wear between two surfaces in relative motion. Oil and grease are commonly used for lubrication.


A device consisting of two or more parts that transform energy into motion. Machines are used to transmit or modify force and motion so as to accomplish some form of useful work.

machining center

A sophisticated, precise machine tool, operated by computer numerical control (CNC), that can perform milling, drilling, tapping, and boring operations at the same location with a variety of tools. A machining center uses a transmission to change the rotary speed and direction of machining tools.

manual transmission

A type of transmission that requires an operator to shift gears manually to change the speed and torque of mechanical energy. Some industrial machines use manual transmission to support a range of operating speeds.

mechanical energy

Energy used to perform work through the physical interaction and motion of tools or machine components. Mechanical energy can be produced in a number of ways.

mechanical system

A collection of machines functioning together to perform useful work. Mechanical systems use a wide range of power transmission components.


The act of interlocking with another object. Gears are designed to mesh with one another in order to transmit mechanical energy.


A hard, strong material with high electric and thermal conductivity. Examples of metal include copper, iron, nickel, and lead.


Positioned at an offset or angle. Misaligned shafts can be connected using a flexible coupling or a universal joint depending on the degree of misalignment between the two shafts.

miter gear set

A type of bevel gear used in pairs with intersecting shafts at 90° angles. In miter gear sets, both the drive gear and driven gear have the same diameter and number of teeth.


A silver-white metal that is resistant to corrosion. Some chains are plated with nickel to resist corrosion.


The process of remaining separate and not meeting, cutting across, or overlapping. Nonintersecting lines are parallel to one another.


A slippery fluid commonly used as an industrial lubricant. Oil is often used in high-speed applications.


A person trained to run a specific type of machine on a daily basis. An operator is required to change gears in a manual transmission.

output device

A power transmission component that performs a mechanical action. An output device receives energy from a power source via power transmission.

output shaft

A rotating shaft that receives power from the mechanical system. Output shafts transfer power from a mechanical system to an output source.


Two lines or axes that are equidistant from each other at all points along their length, and thus never intersect. Many gear trains operate using parallel gear shafts.


The distance around the outside of an object. The perimeter of a circle is also known as its circumference.


Two lines or axes that meet to form right angles. Some angular gear trains operate using perpendicular gear shaft orientation.


A circular gear used in a rack and pinion system to produce linear motion. As the pinion turns, the flat rack slides in a linear direction.


A slender metal fastening device. Pins can be used to connect several different components.


The measure of distance between chain links. Pitch affects the length of a chain's links.

plain bearing

A type of bearing using a sliding motion to reduce friction. Plain bearings are the simplest bearing design.

plain thrust bearing

A type of thrust bearing consisting of two parts: a wedged lower section which reduces friction and accommodates lubrication, and a rotating upper section. Plain thrust bearings are often used along with other plain bearings, such as in crankshafts.

planetary gear trains

A gear train that consists of one or more outer gears rotating around a central gear. Planetary gear trains are also known as epicyclic gear trains.


A lightweight material that typically resists corrosion and is easily shaped. Belts made of plastics can use a range of custom materials for a variety of applications.


Coated or covered with a thin layer of metal. Chains can be plated with various metals to improve durability and corrosion resistance.

point of use

The part of a mechanical system where work is performed. All mechanical systems perform some form of work at a point of use.

positive clutch

A clutch that consists of two mating surfaces with interconnecting elements, such as teeth, that lock together during engagement. Positive clutches do not slip as much during operation as friction clutches.


The rate at which work is accomplished in a specified period of time. Power is expressed as the amount of work accomplished divided by the time it takes to do the work.

power source

A device used to generate the energy that a machine needs to perform work. Power sources include batteries, electric motors, and generators.

power transmission

The movement of energy from a source to an output device that performs work. Power transmission can be performed by mechanical, electrical, and fluid systems.

prime mover

The device that receives one type of energy, converts it to mechanical energy, and delivers it to a mechanical system. Prime movers include electric motors, heat engines, turbines, and electric linear motors.


The outer and inner rings of an antifriction bearing that encase the rolling mechanisms. Races are notched, grooved, or flat.


A flat bar with teeth used in a rack and pinion system to produce linear motion. Racks slide in a linear direction as circular pinions turn against them.

rack and pinion

A gear pair that is used to convert rotary motion into linear motion. A rack and pinion consists of a circular gear, or pinion, that meshes with a flat-toothed bar, or rack.

radial loads

Force that is applied perpendicular to the axis of a bearing's shaft. Radial loads are also called rotary loads.


A number or grade based on predetermined operating standards. Ratings for industrial chains are based on standard measurements and a range of factors related to operation and performance.

retainer clip

A fastener used to secure the parts of a chain link. A retainer clip is also known as a spring clip.

rigid coupling

A type of coupling used to connect shafts that are in alignment. A rigid coupling is the simplest type of coupling.

roller chain

The most common type of chain used in industry. A roller chain can be used at high speeds.

rolling-element bearing

A bearing with rolling parts inside that support the motion of a load. Rolling-element bearings are also called antifriction bearings.

rotary motion

Spinning or turning motion that takes place around an axis, without a change in linear position. Rotary motion is produced by many prime movers and power transmission components.


A rotating component attached to the input shaft on an electromagnetic clutch. The rotor is magnetized when the clutch is engaged.


An elastic material made from the latex sap of the rubber tree. Rubber is commonly used in belts due to its ability to resist water and other conditions.


A device used with bearings to retain lubricant and prevent contamination. Seals can be damaged if the proper lubricant is not applied, resulting in shorter service life.

serpentine belt drives

A belt drive that includes more than two fixed pulleys and requires a belt that can twist around corners. Many serpentine belt drives require flexible belts, such as flat belts.

service life

The length of time an industrial component is expected to be in operation before being replaced. Service life of bearings can be extended through proper lubrication and maintenance practices.


A cylindrical bar used to support rotating components in a mechanical system. Shafts also transmit mechanical energy and motion.


A jarring impact force caused by sudden acceleration, deceleration, or collision. Shock can cause damage to mechanical system components.

side load

A force that pushes sideways against a rotating gear shaft's axis when gears are meshed together at an angle. Side load can lead to deflection and wear.

silent chain

A type of chain with teeth on its links that mesh with teeth in the sprockets of a chain drive. A silent chain, or inverted-tooth chain, operates quietly and smoothly.


A condition that occurs when the load causes the belt to slide out of proper position on the pulley. Slip is most common with flat belt designs.


The rate at which an object travels. Speed is calculated by dividing the distance traveled by the time elapsed.


A rotating component of a machine tool, such as a drill press or milling cutter. Many spindles are operated by gear trains.

spring clip

A fastener used to secure the parts of a chain link. A spring clip is also known as a retainer clip.


A wheel with metal teeth that mesh with the links of a chain. Sprockets are used in chain drive systems to transmit motion.

spur gear

A type of gear that has straight, flat-topped teeth set parallel to the shaft. Spur gears are the most common industrial gears.

stainless steel

An alloy steel that is designed to resist corrosion. Stainless steel chains are used in operations when sanitary conditions are critical.


A predetermined value or specification for design or operation. Industrial chains are manufactured according to standards established by the American National Standards Institute.

surface area

The total area of all outer surfaces of an object. The surface area of an object is calculated differently depending on the shape of the object.

synchronous belt

A toothed belt that meshes with the grooves of a pulley in a synchronous belt drive. Synchronous belts, or timing belts, maintain constant speed during power transmission, and they do not slip.


Gradually decreasing in size from one end of the object to the other. Tapered gear teeth are usually widest at their outer part.


A pulling force that is directed away from the object and attempts to move, stretch, or elongate the object. Belt drive systems must operate under proper tension to transfer power effectively.

thermal energy

A form of power resulting from the movement of particles that is transferred as heat. Thermal energy can be converted into other forms of energy, such as mechanical energy.


A long, spiral ridge around the exterior or interior of a cylindrically shaped object. Threads are used to fasten or provide motion.


A raised, helical ridge around the interior or exterior of a cylindrically shaped object. Threads on a worm mesh with teeth on a worm gear to transfer energy.

thrust ball bearing

A type of ball bearing designed specifically to handle thrust load. Thrust ball bearings use washers instead of inner and outer races to contain the cage.

thrust bearing

A type of bearing designed to reduce friction by carrying thrust or axial loads. Thrust bearings can be plain or rolling-element bearings.

thrust collar

A component often coupled with a thrust bearing to help support axial load. Thrust collars are typically used with plain thrust bearings.

thrust load

Force that is applied parallel to the bearing's axis. Thrust loads are also called axial or linear loads.

timing belt

A toothed belt that meshes with the grooves of a pulley in a synchronous belt drive. Timing belts, or synchronous belts, maintain constant speed during power transmission, and they do not slip.


A force that produces rotation. Gears can transmit high levels of torque.

torque converter

A device that transfers energy from a power source to transmission components. Torque converters are used in automatic transmissions in place of a manual clutch.


The ability of a component to apply a gripping or pulling force through friction. Traction allows belt drives to grip against driven pulleys to transfer mechanical energy.


A machine that uses a combination of gears and other mechanical components to change the speed or torque of mechanical energy. Some transmissions can also change the direction of mechanical energy.


A type of coupling used to transmit power between shafts that are too far out of alignment to be joined by a flexible coupling. A U-joint is also known as a universal joint.

universal joint

A type of coupling used to transmit power between shafts that are too far out of alignment to be joined by a flexible coupling. A universal joint is also known as a U-joint.


A belt with a flat bottom and tapered sides that transmits motion between two pulleys. Multiple V-belts are often used together in order to increase carrying power.

V-belt pulley

A pulley with grooves designed to hold a V-belt. V-belt pulleys can be designed for one or multiple V-belts.


A thin disc with a hole in the middle used to support load when using bearings or fasteners. Washers are used to support thrust ball bearings.


The erosion of material as a result of friction. Helical gears can experience faster wear than other gears due to side loads.


The result of force applied to an object over a distance. Work is accomplished in mechanical systems through the transfer of energy and motion.


The machine component that supports the workpiece and any workholding devices during machining. Worktables use bearings to reduce friction between contacting surfaces.


A cylindrical, screw-shaped shaft that is used with a worm gear to transmit motion. Worms can be designed to fit spur or helical style gear teeth.

worm gear

A gear with teeth that mesh with the screw-like threads of a shaft, called a worm, to transmit motion. Worm gears are usually the driven gears in worm gear sets.

worm gear sets

A worm gear used in combination with a worm. Worm gear sets are used to transmit power between nonintersecting shafts at right angles to one another.