What is the difference between a bridle and a spreader beam?

Where the horizontal component of the sling force ends up. Both carry the same vertical load and both produce the same inward pull at each lift point. A spreader beam resists that pull in a member designed for it, with a compression check and a utilisation. A bridle has no beam, so the only thing between the lift points is the load itself, and the load is in compression whether or not anybody checked it.

How big is the compression a bridle puts into the load?

The vertical share divided by the tangent of the sling angle from horizontal, at each lift point. On the worked 12 t lift that is 34 kN at 60 degrees, 59 kN at 45 and 102 kN at 30. At 45 degrees the inward pull exactly equals the vertical share, and below that it exceeds it. For a slender item those numbers are not small: at 30 degrees the pull reaches 46 percent of the illustrative item's elastic buckling load, before any factor.

When should I use a bridle instead of a spreader beam?

When the load is genuinely stiff between its lift points, when those points are close together, and when headroom is plentiful while beam handling is not. A skid frame or a machine on a fabricated bedplate absorbs the compression without noticing. Use a spreader when the load is slender, long or fragile, when the lift points cannot take a horizontal force, or when headroom is short - because low headroom is exactly what makes the inward pull large.

Who checks the load for the compression a bridle applies?

Whoever owns the load's design, and this is where it fails, because the lifting engineer's scope usually ends at the attachment and the equipment designer's scope is the operating condition. The fix is procedural: state the reactions the rigging delivers into the load as an output of the lifting calculation, with force, direction and point of application; name who receives them; and get an answer in writing. Silence is not acceptance.

Does the sling angle matter more for a bridle than a spreader?

The physics is identical and the consequence is not. On a spreader a flatter angle raises the compression in a member that was sized for compression, and the worked beam takes 98 kN at 12 percent of its capacity. On a bridle the same 98 kN goes into a load that was never designed as a strut. Check the flattest angle the rigging can actually reach, because longer slings and less headroom are both procurement outcomes rather than design decisions.

Bridle sling compression goes into the load

The short answer

A bridle and a spreader carry the same vertical load and put the horizontal component in completely different places. A spreader puts it in a beam designed for it; a bridle puts it in the load.
On the worked 12 t lift the inward pull is 34 kN at 60 degrees and 102 kN at 30. Nothing on a normal lifting calculation looks at either number.
For a slender item that compression is not small. At 30 degrees it reaches 46 percent of the illustrative item's own elastic buckling load, before any factor is applied.
The bridle's advantage is real: it needs no beam, no beam handling and no beam weight, and it costs headroom instead. Choose it knowingly rather than by default.
If you use a bridle, somebody has to check the load in compression, and that somebody is usually not the lifting engineer.

Where the horizontal component goes

It is the same force in both arrangements. The difference is which structure receives it, and whether that structure was designed knowing about it.

Two lift points, one hook above them, two sling legs at an angle.

Leg tension and inward pull

T H = \frac{V}{sin θ} = T cos θ = \frac{V}{tan θ}

$V$: is the vertical share this leg carries
$θ$: is the leg's angle from the horizontal

That inward force has to be resisted by something.

On a spreader beam it is resisted by the beam. The beam is in compression along its length, that compression is a check somebody performed, and the beam was sized for it. The compression is designed for and it is visible on a calculation.

On a bridle there is no beam. The two inward forces pull the lift points towards each other, and the only thing between them is the load itself. The load is in compression, and the load's designer almost certainly did not know it would be.

That is the whole subject. The force is identical in both cases; what differs is whether anything checked it.

On this 12 t lift the inward pull is 58.9 kN at each lift point. On a spreader that force goes into the beam. On a bridle it goes into whatever is between the lift points.

Pricing the compression

It is one over the tangent of the angle, times the vertical share. At 45 degrees it equals the share; below that it exceeds it, and it exceeds it quickly.

For the worked lift, 12 t on two lift points 6.0 m apart:

Sling angle	Leg tension	Inward pull	Headroom needed	Share of the item's buckling load
60°	68.0 kN	34.0 kN	5.20 m	15%
50°	76.8 kN	49.4 kN	3.58 m	23%
45°	83.2 kN	58.9 kN	3.00 m	27%
40°	91.6 kN	70.1 kN	2.52 m	32%
35°	102.6 kN	84.1 kN	2.10 m	38%
30°	117.7 kN	101.9 kN	1.73 m	46%

The last column needs its assumption stated. It compares the inward pull with the classical elastic buckling load of an illustrative slender item: 6.0 m long, pinned at its ends, with a second moment of area of $4.0 \times 1 0^{6} mm^{4}$ in steel, giving 219.3 kN. That is an upper bound and a real item's capacity is lower, because the elastic buckling load ignores yielding, initial imperfection and any eccentricity in how the compression is applied.

Even against that generous benchmark, at 30 degrees the bridle is pushing 46 percent of the item's buckling load through it. Against a realistic design capacity it would be considerably more than that.

Inward pull and headroom against sling angle12 t on two lift points 6.0 m apart

Inward pull (kN)
Headroom needed (m x 10)

Where the same force goes on a spreader

Into a member with a compression check, a buckling curve and a utilisation. That is not a small difference: it is the difference between a designed load path and an undesigned one.

Spreader Beam Design Calculator · computed at page render

The same lift on a spreader at 60 degrees

A 10 t arrangement on a 6 m circular hollow section. The inward force is now an axial compression in the beam.

Axial force in the beamthe inward pull, now in a member	30.7 kN compression
Axial compression checka buckling check on a real section	3.7%
Padeye attachment weld	55.7%

Governing check: Sling angle within declared limits75.9% utilisationPass

Three and a bit percent. A tube designed as a strut carries this force easily, and it is a small number precisely because somebody chose a member to carry it. The same force into an item nobody sized for it is the same force.

Open this example in the calculator

Spreader Beam Design Calculator · computed at page render

The same spreader with the slings flattened

Hook lowered to a nominal 30 degree geometry. This is what a bridle at the same angle would be putting into the load.

Axial force in the beamagainst 30.7 kN at 60 degrees	98.0 kN
Axial compression checkthe beam absorbs it comfortably	11.8%
Padeye attachment weldthe attachment does not	148.2%
Sling angle limit	161.8%

Governing check: Sling angle within declared limits161.8% utilisationFail

The beam takes 98 kN of compression at 12 percent of its capacity. That is a little under the table's 102 kN because the solver measures the angle where the sling pin actually is, above the beam axis, rather than at the nominal 30 degrees. Either number in a slender load is approaching half its elastic buckling load, and a beam chosen for compression and an item that happens to be in the way are not comparable structures.

Open this example in the calculator

One is a designed strut and one is a load that never expected to be a strut. The force is identical; only the receiving structure is different.

When a bridle is the right answer

Often. It is lighter, simpler and quicker, and the compression only matters when the load cannot take it.

Use a bridle when the load is genuinely stiff between its lift points. A skid frame, a stiff base, a machine on a fabricated bedplate. The compression is real and the structure eats it without noticing.

Use a bridle when the lift points are close together. The inward force depends on the angle, and short spans reach steep angles without much headroom.

Use a bridle when headroom is plentiful and beam handling is not. A spreader has to be transported, stored, lifted into place and rigged. On a small lift that is more work than the beam saves.

Use a spreader when the load is slender, long or fragile. Vessels, ducting, long fabrications, anything with a shell rather than a frame between its lift points.

Use a spreader when the lift points cannot take a horizontal force. Some attachments are designed for a vertical pull and nothing else, and a bridle puts a large horizontal component into them.

Use a spreader when headroom is short. The bridle's inward force is the price of low headroom, and below about 45 degrees that price rises fast.

Before choosing a bridle

01Compute the inward pullVertical share divided by the tangent of the angle, at each lift point.
02Identify what resists itName the member or the structure between the lift points. If you cannot name it, that is the finding.
03Give the compression to whoever owns that structureWith the force, the direction and where it is applied. The lifting calculation ends at the attachment.
04Check the attachments for horizontal loadA lift point designed for a vertical pull is not automatically adequate for a large lateral one.
05Check the flattest angle the rigging can reachLonger slings and less headroom both flatten it, and both are procurement outcomes.
06State a minimum sling angle on the planAs an acceptance criterion a rigger can fail, in the horizontal convention.

Whose check it is

Not the lifting engineer's, usually, and that is exactly why it goes missing.

The compression in the load is a structural check on the load. The lifting engineer computes the force and hands it over; whoever owns the load's design accepts it or does not.

That handover is where it fails. On a typical project the lifting engineer's scope ends at the attachment, the equipment designer's scope is the operating condition, and the lifting condition sits between them belonging to nobody. The fix is procedural and it is cheap:

State the reactions the rigging delivers into the load, as an output. Force, direction and point of application, at every lift point, on the lifting calculation.

Name who receives them. By role at minimum, with a date.

Get an answer in writing. "The item is adequate for a 102 kN axial compression applied at the lift points" is a sentence somebody signs. Silence is not acceptance.

Five ways a bridle goes wrong

All five are the horizontal component, arriving somewhere nobody was looking.

1. The compression never computed. The commonest, and the whole reason for this article.

2. Computed and never handed over. A number on a lifting calculation that nobody with authority over the load ever saw.

3. The lift points checked for tension only. A large horizontal component into an attachment designed for a vertical pull.

4. The nominal angle used. The built angle is flatter, because slings are longer and headroom shorter than planned, and the inward force rises faster than the angle falls.

5. A bridle chosen because a spreader was not available. A legitimate constraint that becomes a defect the moment nobody reprices the compression it introduces.

Common questions

What is the difference between a bridle and a spreader beam?: Where the horizontal component of the sling force ends up. Both carry the same vertical load and both produce the same inward pull at each lift point. A spreader beam resists that pull in a member designed for it, with a compression check and a utilisation. A bridle has no beam, so the only thing between the lift points is the load itself, and the load is in compression whether or not anybody checked it.
How big is the compression a bridle puts into the load?: The vertical share divided by the tangent of the sling angle from horizontal, at each lift point. On the worked 12 t lift that is 34 kN at 60 degrees, 59 kN at 45 and 102 kN at 30. At 45 degrees the inward pull exactly equals the vertical share, and below that it exceeds it. For a slender item those numbers are not small: at 30 degrees the pull reaches 46 percent of the illustrative item's elastic buckling load, before any factor.
When should I use a bridle instead of a spreader beam?: When the load is genuinely stiff between its lift points, when those points are close together, and when headroom is plentiful while beam handling is not. A skid frame or a machine on a fabricated bedplate absorbs the compression without noticing. Use a spreader when the load is slender, long or fragile, when the lift points cannot take a horizontal force, or when headroom is short - because low headroom is exactly what makes the inward pull large.
Who checks the load for the compression a bridle applies?: Whoever owns the load's design, and this is where it fails, because the lifting engineer's scope usually ends at the attachment and the equipment designer's scope is the operating condition. The fix is procedural: state the reactions the rigging delivers into the load as an output of the lifting calculation, with force, direction and point of application; name who receives them; and get an answer in writing. Silence is not acceptance.
Does the sling angle matter more for a bridle than a spreader?: The physics is identical and the consequence is not. On a spreader a flatter angle raises the compression in a member that was sized for compression, and the worked beam takes 98 kN at 12 percent of its capacity. On a bridle the same 98 kN goes into a load that was never designed as a strut. Check the flattest angle the rigging can actually reach, because longer slings and less headroom are both procurement outcomes rather than design decisions.

Sources

Every document below is linked at its publisher or regulator. Xarpis reproduces no standard text; where a clause is named, the identifier is given so you can find it in your own copy.

ASME B30.9Slings
ASME · paid document
The US volume covering alloy steel chain, wire rope, metal mesh, synthetic rope, synthetic webbing and synthetic round slings: rated loads, marking, inspection, and the removal criteria that decide when a sling leaves service. Where published sling rated loads and angle reductions come from.
LOLER 1998Lifting Operations and Lifting Equipment Regulations
UK Health and Safety Executive · free to read
The UK duty framework for lifting operations: planning by a competent person, supervision, and thorough examination of lifting equipment and accessories. Like OSHA's rules it governs the process, not the arithmetic.
ASME BTH-1Design of Below-the-Hook Lifting Devices
ASME · paid document
Structural, mechanical and electrical design criteria for below-the-hook lifting devices, used alongside ASME B30.20 which carries the safety requirements. The current edition is BTH-1-2023; Xarpis implements the 2020 edition and says so on every result.
EN 13155Cranes. Safety. Non-fixed load lifting attachments
BSI (national adoption of the CEN standard) · paid document
The harmonised European standard for non-fixed load lifting attachments - the family a spreader beam or lifting beam belongs to. It carries the load basis and the proof requirements, not member resistances, which is why an EN route needs EN 1993 alongside it. Now published as EN 13155:2020+A1:2025.

Run the check properly

Reading about a calculation is not the same as being able to hand one over. These tools produce the traceable record.

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