A trunnion is a cylindrical protrusion used as a mounting and/or pivoting point. In a cannon
A cannon is any piece of artillery that uses gunpowder or other usually explosive-based propellents to launch a projectile. Cannon vary in caliber, range, mobility, rate of fire, angle of fire, and firepower; different forms of cannon combine and balance these attributes in varying degrees,...

, the trunnions are two projections cast just forward of the centre of mass of the cannon and fixed to a two-wheeled movable gun carriage. As they allowed the muzzle to be raised and lowered easily, the integral casting of trunnions is seen by military historians as one of the most important advances in early field artillery
Field artillery
Field artillery is a category of mobile artillery used to support armies in the field. These weapons are specialized for mobility, tactical proficiency, long range, short range and extremely long range target engagement....


Medieval history

With the creation of larger and more powerful siege guns in the early 1400s, a new way of mounting them had to be specially designed. Stouter gun carriages were created with reinforced wheels, axles, and “trails” which extended behind the gun. Guns would be up to eight feet in length and shoot iron projectiles weighing from twenty-five to fifty pounds. These wrought iron
Wrought iron
thumb|The [[Eiffel tower]] is constructed from [[puddle iron]], a form of wrought ironWrought iron is an iron alloy with a very low carbon...

 balls when discharged were comparable in range and accuracy with stone-firing bombards.

Trunnions were mounted near the center of mass to allow the barrel to be elevated to any desired angle, without having to dismount it from the carriage upon which it rested. Some guns had a second set of trunnions placed several feet back from the first pair, which could be used to allow for easier transportation. The gun would recoil causing the carriage to move backwards several feet but men or a team of horses could put it back into firing position. It became easier to rapidly transport these large siege guns, maneuver them from transportation mode to firing position, and could go wherever a team of men or horses could pull them.

Initial significance

Due to its capabilities, the French and Burgundy designed siege gun, equipped with its trunnions, required little significant modification from around 1465 to the 1840s.

King Charles VIII
Charles VIII of France
Charles VIII, called the Affable, , was King of France from 1483 to his death in 1498. Charles was a member of the House of Valois...

 and the French army used this new gun in the 1494 invasion of Italy. Although deemed masters of war and artillery at that time, Italians had not anticipated the innovations in French siege weaponry. Prior to this, field artillery guns were huge, large-caliber bombards: superguns that, along with enormous stones or other projectiles, were dragged from destination to destination. These behemoths could only be used effectively in sieges, and more often than not provided just a psychological effect on the battlefield; owning these giant mortar
Mortar (weapon)
A mortar is an indirect fire weapon that fires explosive projectiles known as bombs at low velocities, short ranges, and high-arcing ballistic trajectories. It is typically muzzle-loading and has a barrel length less than 15 times its caliber....

s did not guarantee any army a victory. The French saw the limitations of these massive weapons and focused their efforts on improving their smaller and lighter guns, which used smaller, more manageable projectiles combined with larger amounts of gunpowder. Equipping them with trunnions was key for two reasons: teams of horses could now move these cannons fast enough to keep up with their armies, without having to stop and dismount them from their carriages to achieve the proper range before firing. Francesco Guicciardini
Francesco Guicciardini
Francesco Guicciardini was an Italian historian and statesman. A friend and critic of Niccolò Machiavelli, he is considered one of the major political writers of the Italian Renaissance...

, an Italian historian and statesman, sometimes referred to as the “Father of History,” wrote that the cannons were placed against town walls so quickly, spaced together so closely and shot so rapidly and with such force that the amount of damage inflicted went from a matter of days (as with bombards) to a matter of hours. For the first time in history, as seen in the 1512 battle of Ravenna
Battle of Ravenna (1512)
The Battle of Ravenna, fought on 11 April 1512, by forces of the Holy League and France, was a major battle of the War of the League of Cambrai in the Italian Wars...

 and the 1515 Battle of Marignano
Battle of Marignano
The Battle of Marignano was fought during the phase of the Italian Wars called the War of the League of Cambrai, between France and the Old Swiss Confederacy. It took place on September 13 and 15, 1515, near the town today called Melegnano, 16 km southeast of Milan...

, artillery weaponry played a very decisive part in the victory of the invading army over the city under siege. Cities that had proudly withstood sieges for up to seven years fell swiftly with the advent of these new weapons.

Defensive tactics and fortifications had to be altered since these new weapons could be transported so speedily and aimed with much more accuracy at strategic locations. Two such changes were the additions of a ditch and low, sloping ramparts of packed earth that would surround the city and absorb the impact of the cannon balls and the replacement of round watchtowers with angular bastion
A bastion, or a bulwark, is a structure projecting outward from the main enclosure of a fortification, situated in both corners of a straight wall , facilitating active defence against assaulting troops...

s. These towers would be deemed trace Italienne.

Whoever could afford these new weapons had the tactical advantage over their neighbors and smaller sovereignties, which could not incorporate them into their army. Smaller states, such as the principalities of Italy, began to conglomerate. Preexisting stronger entities, such as France or the Hapsburg
Habsburg Monarchy
The Habsburg Monarchy covered the territories ruled by the junior Austrian branch of the House of Habsburg , and then by the successor House of Habsburg-Lorraine , between 1526 and 1867/1918. The Imperial capital was Vienna, except from 1583 to 1611, when it was moved to Prague...

 emperors, were able to expand their territories and maintain tighter control. With the threat of their land and castles being seized, the nobility began to pay their taxes and more closely follow their ruler’s mandates. With siege guns mounted on trunnions, stronger and larger states were formed, but because of this, struggles between neighboring governments with consolidated power began to ensue and would continue to plague Europe for the next few centuries.

In firearms

  • On firearm
    A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...

    s, the barrel
    Gun barrel
    A gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity....

     is sometimes mounted in a trunnion, which in turn is mounted to the receiver
    Receiver (firearms)
    In firearms terminology, the receiver is the part of a firearm that houses the operating parts. The receiver usually contains the bolt carrier group, trigger group, and magazine port. In most handguns, the receiver, or frame, holds the magazine well or rotary magazine as well as the trigger mechanism...

    . This usage is common for tubular or pressed metal frame guns, such as the AK-47
    The AK-47 is a selective-fire, gas-operated 7.62×39mm assault rifle, first developed in the Soviet Union by Mikhail Kalashnikov. It is officially known as Avtomat Kalashnikova . It is also known as a Kalashnikov, an "AK", or in Russian slang, Kalash.Design work on the AK-47 began in the last year...

    , PPSh-41
    The PPSh-41 was a Soviet submachine gun designed by Georgi Shpagin as an inexpensive, simplified alternative to the PPD-40. Intended for use by minimally-trained conscript soldiers, the PPSh was a magazine-fed selective-fire submachine gun using an open-bolt, blowback action...

    , Uzi, Sten
    The STEN was a family of British 9 mm submachine guns used extensively by British and Commonwealth forces throughout World War II and the Korean War...

    , and others.

In vehicles

  • In older cars, the trunnion is part of the suspension and either allows free movement of the rear wheel hub in relation to the chassis or allows the front wheel hub to rotate with the steering. On many cars (such as those made by the Triumph Motor Company) the trunnion is machined from a brass or bronze casting and is prone to failure if not greased properly. American Motors
    American Motors
    American Motors Corporation was an American automobile company formed by the 1954 merger of Nash-Kelvinator Corporation and Hudson Motor Car Company. At the time, it was the largest corporate merger in U.S. history.George W...

     used a molded rubber "Clevebloc" bushings on the upper trunnion to seal out dirt and retain silicone lubricant for the life of the car.
  • In aviation, the term refers to the structural component that attaches the undercarriage
    The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land...

     or landing gear to the airframe. For aircraft equipped with retractable landing gear, the trunnion is pivoted to permit rotation of the entire gear assembly.
  • In heavy equipment, such as a bulldozer
    A bulldozer is a crawler equipped with a substantial metal plate used to push large quantities of soil, sand, rubble, etc., during construction work and typically equipped at the rear with a claw-like device to loosen densely-compacted materials.Bulldozers can be found on a wide range of sites,...

    , the term refers to the protrusions on the vehicle frame on which the blade frame attaches and hinges allowing vertical movement.
  • In Chevrolet GMC C/K pickup trucks
    Chevrolet C/K
    The C/K is the name for Chevrolet and GMC's full-size pickup truck line from 1960 until 1999 in the United States, from 1965 to 1999 Canada, from 1964 through 2001 in Brazil, and from 1975 to 1982 in Chile. The first Chevrolet pickup truck appeared in 1924, though in-house designs did not appear...

    , the term refers to the tailgate attachment points. Rather than using conventional tailgate hinges, trunnions are used to permit quick toolless removal and installation of the pickup tailgate.
  • In trailers, the term refers to the type of suspension used on a two axle configuration with eight tires, i.e. four tires per axle. This type of trailer suspension is commonly used in the western United States and allows 60000 pounds (27,215.5 kg) to be loaded on that axle group.
  • In the valve train of a pushrod engine, the term refers to the fixed axle that acts as a pivot point for the valve rocker.

In other technology

  • In steam engines, they are supporting gudgeon pins on either side of an oscillating steam cylinder
    Cylinder (engine)
    A cylinder is the central working part of a reciprocating engine or pump, the space in which a piston travels. Multiple cylinders are commonly arranged side by side in a bank, or engine block, which is typically cast from aluminum or cast iron before receiving precision machine work...

    . They are usually tubular and convey steam.
  • On communication satellites, the antennas
    Antenna (radio)
    An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

     are usually mounted on a pair of trunnions to allow the beam pattern to be correctly pointed on the Earth from the geostationary orbit
    Geostationary orbit
    A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...

  • On stage lighting instrument
    Stage lighting instrument
    Stage lighting instruments are used in stage lighting to illuminate theatrical productions, concerts, and other performances taking place in live performance venues. They are also used to light television studios and sound stages.Many stagecraft terms vary between the United States and the United...

    s, a trunnion is a bracket attached to both ends of a striplight
    A striplight is a multi-circuit stage lighting instrument. Striplights are one of the most basic types of lighting fixtures available. They usually consist of row of lamps. A single striplight is usually wired internally into either 3 or 4 circuits. Each internal circuit consists of several...

     that allows the striplight to be mounted on the floor. Sometimes trunnions are also equipped with casters to allow the striplight to be moved easily.
  • In woodworking
    Woodworking is the process of building, making or carving something using wood.-History:Along with stone, mud, and animal parts, wood was one of the first materials worked by early humans. Microwear analysis of the Mousterian stone tools used by the Neanderthals show that many were used to work wood...

    , they are the assembly that holds a saw's arbor to the underside of the saw table.
  • In Waste Collection the trunnion is the bar on the front of a Dumpster that connects to the back of a garbage truck.
  • On the Space Shuttle
    Space Shuttle
    The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

    , trunnion pins are affixed to the sides of payload items allowing them to be secured to receivers mounted on the sills of the payload bay. These receivers can be remotely commanded to secure and release selected items. Similar keel pins protrude from the nadir side of payload items, into matching holes in the bottom of the payload bay.
  • On hydraulic cylinders, a trunnion (either featuring external pins or internal pockets) can be an alternative body mounting type, as opposed to a flange or pin eye.
  • In steelmaking, on the Bessemer converter. There are trunnions on either side to be able to pour the molten steel out.
  • In surveying
    See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...

     total station
    Total station
    A total station is an electronic/optical instrument used in modern surveying. The total station is an electronic theodolite integrated with an electronic distance meter to read slope distances from the instrument to a particular point....

    s and theodolite
    A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology...

    s, the trunnion axis is the axis about which the telescope
    A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

    -Transportation:* Ford Transit, a van made by the Ford Motor Company* Mass transit, public transport systems in which passengers are carried in large numbers* Navigational transit, when a navigator observes two fixed reference points in line...

    s. It is parallel to the horizontal axis defined by the tubular spirit bubble.
  • In Dobsonian telescope designs.
  • In structural engineering, a type of Bascule bridge
    Bascule bridge
    A bascule bridge is a moveable bridge with a counterweight that continuously balances the span, or "leaf," throughout the entire upward swing in providing clearance for boat traffic....

    , with the road deck on one side of the trunnion, and the counterweight on the other.
  • In laboratory centrifuges, trunnions are used to pivot sample buckets in swinging-bucket rotors.
  • In nuclear power plants, when the steam generators are replaced, trunnions are used to upend them, to get them on the rail system, to shuttle them out of containment.

Trunnion bearings

In avionics
Avionics are electronic systems used on aircraft, artificial satellites and spacecraft.Avionic systems include communications, navigation, the display and management of multiple systems and the hundreds of systems that are fitted to aircraft to meet individual roles...

, these are self-contained concentric bearings that are designed to offer fluid movement in a critical area of the steering.

The term is also used to describe the wheel that a rotating cylinder runs on. For example, a lapidary (stone-polishing) cylinder runs on a pair of rollers, similar to trunnions. The sugar industry uses rotating cylinders up to 22 feet (7 m) in diameter, 131 ft (40 m) long, and weighing around 1,000 tons. These rotate at around 30 revolutions per hour. They are supported on a pathring which runs on trunnions. Similar devices called rotary kiln
Rotary kiln
A Rotary kiln is a pyroprocessing device used to raise materials to a high temperature in a continuous process. Materials produced using rotary kilns include:* Cement* Lime* Refractories* Metakaolin* Titanium dioxide* Alumina* Vermiculite...

s are used in cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...


In mining, some refining plants utilise drum scrubbers in the process that are supported by a large trunnion and associated trunnion bearings at each end.
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