The Key Components of the Crane

The parts of a crane are the components that support a load, lift it and move it horizontally. They include a structure such as a boom, jib or girder, a hoisting mechanism, a hook, a slewing or travelling mechanism, and a support that keeps the crane stable. A power and control system and a set of safety devices complete the list, and every crane has some version of each group. What changes from one type to the next is how each part is built, so the parts of a truck mounted crane look very different from the parts of an overhead crane in a factory.

We have built truck mounted cranes in Xuzhou since 2003, and this guide replaces a short 2022 article that described overhead crane parts only. It now covers the crane components shared by all designs first. It then describes the parts of each principal crane type, from truck mounted knuckle boom and telescopic cranes to tower, overhead, jib and marine cranes, before closing with a glossary of crane terminology. Where we do not build a type, we say so plainly.

What are the main parts of a crane?

The US general industry rule defines a crane as “a machine for lifting and lowering a load and moving it horizontally, with the hoisting mechanism an integral part of the machine” [1]. That definition already names the two jobs every crane must do. To do them, every design needs the same seven component groups.

1. Structure. The member that carries the load away from the support: a boom on a mobile crane, a jib on a tower crane, a bridge girder on an overhead crane.
2. Hoisting mechanism. The component that raises and lowers the load. The US construction rule defines a hoist as “a mechanical device for lifting and lowering loads by winding a line onto or off a drum” [2]. On a knuckle boom crane, hydraulic cylinders often do this work instead of a drum.
3. Hook and load block. The point where slings, chains or a lifting beam are attached, often with a safety latch that keeps the sling seated in the hook.
4. Slewing or travel. The parts that move the load sideways: a slewing bearing and drive that turn the crane, or wheels and rails that move it.
5. Support. Outriggers, tracks, a pedestal, a foundation or a runway that carries the crane and its load into the ground or the building, and that largely determines how stable the crane remains at a given radius.
6. Power and controls. A hydraulic system, an electric drive or an engine, plus the levers, pendant or remote control the operator uses.
7. Safety devices. Limiters, indicators, holding valves, stops and switches that keep the crane inside its rated capacity.

During a lift, these groups work in a fixed order. The support is set up first, and the structure is then positioned so that the hook is above the load. The hoisting mechanism takes the weight, the slewing or travel mechanism moves the load horizontally to its destination, and the safety devices monitor the operation throughout. The table compares how the same component group appears on three very different machines.

Component group	Truck mounted crane	Tower crane	Overhead (bridge) crane
Structure	Boom: folding or telescopic	Mast and horizontal jib	Bridge girder(s)
Hoisting mechanism	Boom cylinders, or a hydraulic winch and wire rope	Hoist drum and wire rope	Electric hoist with rope or chain
Hook and block	Hook at the boom tip or on a hook block	Hook block under the trolley	Load block under the hoist
Sideways movement	Slewing bearing and slewing drive	Slewing unit and trolley on the jib	Trolley travel and bridge travel
Support	Base, outrigger beams and legs	Foundation or base	End trucks on a runway
Power and controls	Truck PTO, pump, control valve	Electric drives, cab controls	Electric drives, pendant or remote

Crane anatomy: parts of a truck mounted knuckle boom crane

A knuckle boom crane is a hydraulic crane whose boom folds at a hinge, called the knuckle, so it can stow in a small space behind the truck cab. The US rule calls it an articulating crane, one “whose boom consists of a series of folding, pin connected structural members, typically manipulated to extend or retract by power from hydraulic cylinders” [2]. The diagram below identifies its principal components, numbered from the outrigger legs up to the hook.

Read from the ground upwards, the crane operates in a logical sequence. The outrigger legs push down onto pads, so the load goes into the ground rather than through the truck’s tyres. The base bolts to the chassis and carries the outrigger beams, the oil tank and the control valve. On top of it, the slewing bearing and slewing drive rotate the column. The main boom cylinder raises the main boom, and the outer boom cylinder opens the outer boom at the knuckle. Finally, the telescopic extensions slide out of the outer boom to add reach.

Our 10 t SQ10ZA4 shows these parts on a real crane, and its drawing gives a maximum lifting capacity of 10,000 kg, a lifting moment of 21 t·m and a full 360° of rotation. The reach runs from 4,442 mm to 10,495 mm, and the outrigger span runs from 2,499 mm to 5,799 mm. Smaller cranes can differ: our 800 kg SQ08ZA3 rotates through 330°, not a complete circle. For each part’s function, the hydraulic figures and a spare parts list, read our guide to truck mounted crane parts. Our article on what a knuckle boom crane is explains how the folding boom works.

What changes on a telescopic truck mounted crane

A telescopic crane keeps the same lower half: outriggers, base, slewing bearing and column. Above the column, it has one straight boom made of nested sections that slide out of each other. A single luffing cylinder raises the boom, and a hydraulic winch lifts the hook on a wire rope that runs over sheaves at the boom head. Our 2 t SQ2SA3 has boom lengths from 3.4 m to 8.5 m, while our 20 t SQ20SA5 extends from 6.8 m to 22.5 m and is rated for 1,500 kg at a 22.0 m radius.

Because its hook hangs on a rope, a telescopic crane needs several parts that a knuckle crane may not have: the winch drum, the wire rope, the boom head sheaves and a hook block. Our guides on the telescopic boom crane, the crane boom, the crane winch and crane wire rope and sheaves cover each of these in detail.

Mobile crane parts

A large mobile crane, such as an all-terrain or crawler crane, splits into two halves. The lower half is the carrier: a purpose-built truck, a rough-terrain undercarriage or a set of crawler tracks. The upper half, the upperworks, is described in the US rule as “the revolving frame of equipment on which the operating machinery (and many cases the engine) are mounted along with the operator’s cab” [2]. The same definition places the counterweight at the rear of the upperworks and the boom at the front.

• Counterweight: “a weight used to supplement the weight of equipment in providing stability for lifting loads by counterbalancing those loads” [2]. Our crane counterweight guide explains why truck mounted cranes rarely carry one.
• Outriggers: on hydraulic truck mounted cranes, Wikipedia notes, they extend horizontally from the chassis and then vertically to level and stabilise the crane [3]. Read how pad loads are worked out in our article on outriggers and ground bearing pressure.
• Boom: the US rule defines it as “an inclined spar, strut, or other long structural member which supports the upper hoisting tackle” [2].
• Jib: an extension fitted at the boom tip for additional reach, which our article on what a fly jib is describes in detail.
• Slewing ring and drive: they rotate the upperworks, as explained in our guide to crane slewing.

We do not manufacture all-terrain, rough-terrain or crawler cranes, but our overview of the types of cranes shows where each of them fits.

What are the parts of a tower crane?

A tower crane is, under the US rule, a lifting structure “which utilizes a vertical mast or tower to support a working boom (jib) in an elevated position” [2]. The components of a tower crane, as Wikipedia’s crane article lists them, are [3]:

• Base: fixed to a concrete slab or foundation.
• Mast: the main supporting tower of the crane.
• Slewing unit: at the top of the mast, it turns the whole upper crane.
• Jib: the long horizontal arm that carries the load.
• Counter-jib: the shorter arm behind the mast, carrying the motors and concrete counterweights.
• Operator’s cab: on most tower cranes, just above the slewing unit.
• Trolley: it runs along the jib to move the load in and out, with the hook block hanging below, so the radius changes without moving the jib itself.

Tower cranes also carry their own limiting devices, and the US tower crane rule requires a trolley travel limiting device at both ends of the jib together with a load moment limiting device. Tower cranes manufactured after 8 November 2011 also need a hoist drum device that prevents the last 2 wraps of cable from spooling off the drum [4]. We do not manufacture tower cranes of any kind, so these devices are described here for reference only.

Overhead crane parts (bridge crane components)

An overhead crane, also called a bridge crane, is “a crane with a movable bridge carrying a movable or fixed hoisting mechanism and traveling on an overhead fixed runway structure” [1]. It serves a factory bay from above, and the earlier version of this article described four of its parts. Here they are again, corrected and completed with the definitions in 29 CFR 1910.179:

• Hook and load block: the load block is “the assembly of hook or shackle, swivel, bearing, sheaves, pins, and frame suspended by the hoisting rope”. The rule also says hooks must meet the maker’s recommendations and must not be overloaded.
• Hoist: “an apparatus which may be a part of a crane, exerting a force for lifting or lowering”, and it lifts on either wire rope or a load chain.
• Trolley: “the unit which travels on the bridge rails and carries the hoisting mechanism”. Its movement at right angles to the runway is called trolley travel.
• Bridge: the part “consisting of girders, trucks, end ties, footwalks, and drive mechanism which carries the trolley or trolleys”, and bridges are built with either one girder or two.
• End trucks: a truck is “the unit consisting of a frame, wheels, bearings, and axles which supports the bridge girders or trolleys”.
• Runway: “an assembly of rails, beams, girders, brackets, and framework on which the crane or trolley travels”, usually along the two long walls of the building.
• Bumpers, stops and limit switches: bumpers absorb energy at the end of travel, stops limit the travel of the trolley or bridge, and an upper limit switch stops the load block before it hits the hoist.

A gantry crane has the same parts, except that its bridge stands “on two or more legs running on fixed rails or other runway” [1], and we manufacture neither overhead nor gantry cranes.

Jib crane parts

A jib crane is the simplest industrial crane. Wikipedia describes a horizontal arm, the jib, that supports a movable hoist and is fixed to a wall or to a floor-mounted pillar; the jib may swing through an arc or stay fixed [3]. Its components are therefore the pillar or wall bracket, the jib arm, a pivot or slewing bearing, a small trolley that runs along the arm and an electric or manual hoist with its hook. A wall crane that travels on a runway along the columns of a building is a related type in 29 CFR 1910.179, and we do not manufacture either type for workshops.

Do not confuse this industrial jib crane with the jib on a mobile crane, which is an extension at the boom tip. A forklift jib attachment is different again, because it converts a forklift into a small crane for occasional lifting in yards and warehouses.

Marine crane parts

A marine crane uses the same hydraulic layout as a truck mounted crane, but it stands on a pedestal bolted or welded to the deck instead of on outriggers. Above the pedestal sit the slewing bearing and drive, the column, the boom with its cylinders, and usually a winch with a wire rope and hook block, so the hook can reach the water line. The components that change most are the ones exposed to salt water: paint, pins, seals, hoses and electrical parts. Because the pedestal position decides how far the hook can reach over the side, the pedestal and the crane are normally specified together. Our article on the structure of marine cranes walks through each component.

Which safety devices does a crane need?

Safety devices are crane components too, and the regulations identify them individually. For construction cranes in the United States, 29 CFR 1926.1415 requires a crane level indicator, boom stops (except on hydraulic booms) and a horn. Hydraulic outrigger and stabiliser jacks also need an integral holding device or check valve [5]. Operations must not begin unless all of these devices work properly.

The operational aids in 29 CFR 1926.1416 add more: a telescopic boom crane built after 28 February 1992 must have an anti two-block device, which stops the hook block from being pulled into the boom tip [6]. A load moment indicator, as defined in 29 CFR 1926.1401, senses the overturning moment, the load multiplied by the radius, and shows the operator what share of rated capacity is in use [2]. A load moment limiter goes further and cuts power when capacity is reached. On a hydraulic crane, the holding valves on each cylinder perform similar protective work. Our explainer on the hydraulic crane shows their position in the circuit, and our hydraulic system guide covers the PTO, pump and oil.

Crane terminology: a glossary of crane parts

The same part often has two or three different names, depending on the crane type, the manufacturer and the market. This crane terminology table matches the names you will see in manuals, quotations and inspection reports.

Term	Also called	Meaning
Boom	Arm	The inclined structural member that carries the load out from the crane
Jib	Fly jib, extension	An extension at the boom tip; on a tower crane, the horizontal working arm
Knuckle	Articulation, hinge	The joint where a folding boom bends
Column	King post, turret	The upright post that carries the boom pivot on a hydraulic crane
Mast	Tower	The vertical structure of a tower crane
Slewing	Swing, rotation	Turning the crane around its vertical axis
Slewing bearing	Slew ring, turntable bearing	The large bearing that lets the crane turn under load
Luffing	Derricking	Raising or lowering the boom to change the radius
Outrigger	Stabiliser, support leg	A leg that spreads the load into the ground and levels the crane
Counterweight	Ballast	Weight that balances the load and keeps the crane stable
Hoist	Winch	The drum and motor that wind the rope to lift and lower the load
Sheave	Pulley	A grooved wheel that guides the wire rope
Hook block	Load block	The hook with its sheaves and frame, hanging from the rope
Two-blocking	–	The hook block touching the boom tip or upper block
Radius	Outreach, working radius	Horizontal distance from the slewing centre to the hook
Rated capacity	Safe working load	The maximum load the maker permits in a given configuration
Upperworks	Superstructure	The revolving part of a mobile crane
Trolley	Crab	The unit that carries the hoist along a jib or bridge
End truck	End carriage	The wheeled unit at each end of an overhead crane bridge
Runway	Crane rail	The rails and beams an overhead crane travels on

Rated capacity always depends on the working radius, and our guide on how to read a crane load chart shows how to find the correct figure for your lift.

Which crane components need regular inspection?

The components that carry the load or hold it in position need the closest inspection, because a defect in any of them can drop the load or destabilise the crane. They include hooks, wire rope and sheaves, boom pins, cylinders and holding valves, hydraulic hoses, the slewing bearing bolts and the outrigger legs with their pads. In Great Britain, regulation 9 of LOLER 1998 requires lifting equipment exposed to deterioration to be thoroughly examined at least every 12 months, or every 6 months for lifting accessories [7]. The HSE adds that all lifting operations must be properly planned, appropriately supervised and carried out in a safe manner [8].

For the daily and periodic checks that an operator can carry out before work, use our truck mounted crane inspection checklist, and for hook wear limits, read our crane hook guide. No BOB-LIFT crane is designed to lift people, whatever its parts.

Example scenario (an illustration, not a customer record): a building supplier compares a 10 t knuckle boom crane with a 10 t telescopic crane. Both cranes share the same outriggers, base, slewing bearing and column, but the knuckle crane adds a second boom, a knuckle joint and an outer boom cylinder, and lifts at the boom tip. The telescopic crane adds a winch, a wire rope and a hook block instead, so the supplier plans different spare parts: more cylinder seals for the first, a spare rope and sheave checks for the second.

Frequently asked questions

What are the main parts of a crane?

Every crane has a structure (boom, jib or girder), a hoisting mechanism, a hook and load block, and a slewing or travelling mechanism. It also needs a support such as outriggers, a foundation or a runway, together with a power and control system and safety devices.

What is the difference between a boom and a jib?

On a mobile crane, the boom is the main lifting arm and the jib is an extension fitted at its tip. On a tower crane, the jib is the horizontal working arm itself, and the US rule calls it a boom only when it can luff up and down.

What are the parts of an overhead crane called?

The main parts are the bridge girders, the end trucks, the runway, the trolley, the hoist and the hook or load block, plus bumpers, stops and limit switches.

Which part of a crane lifts the load?

The hoisting mechanism lifts the load. On most cranes it is a hoist or winch that winds wire rope onto a drum. On a knuckle boom crane without a winch, the boom cylinders raise the load at the boom tip.

Which crane types does BOB-LIFT make?

We make new truck mounted knuckle boom and telescopic cranes, from the 800 kg SQ08ZA3 up to the 50,000 kg SQZ1000, along with marine cranes. We do not make tower, overhead, gantry, jib, all-terrain or crawler cranes.

How we compiled this guide

We rewrote this guide in November 2026 to replace a 2022 version that listed only four overhead crane parts. The definitions come from the official eCFR text of 29 CFR 1910.179, 1926.1401, 1926.1415, 1926.1416 and 1926.1435, the LOLER text on legislation.gov.uk and the HSE page on lifting operations, all read in November 2026. The tower, jib and loader crane descriptions follow Wikipedia’s crane article. Our own figures come from the current BOB-LIFT technical drawings of the SQ10ZA4, SQ08ZA3, SQ2SA3, SQ20SA5 and SQZ1000. We removed claims from the earlier version that we could not support, such as fixed tonnage limits for chain and rope hoists. Achord Chan, Product Operations Director, reviewed the guide, which does not replace your crane manual or the regulations where you work.

Need the parts drawing for your crane?

Tell us what you lift, the working radius and the truck or vessel the crane will go on. Our engineers will recommend a knuckle boom or telescopic model and send its dimension drawing and load chart, with every main part named. Each new crane carries a 12-month warranty on the whole machine, common spare parts leave the factory within 48 hours, and our service team replies within 12 hours. Contact us for a quotation and the drawings for the model that suits your work.