KEVOS® MAKEOS · Mechanics
Eyebolt Lift Check (Unequal Leg Tensions, Angled Capacity, Thread Engagement)
When a load hangs from two eyebolts with legs at different angles, what tension does each eyebolt actually carry, is that within its capacity at the angle, and is each eyebolt screwed in deeply enough?
Check of a two-eyebolt lift with legs at unequal angles to the vertical: the tension in each leg from horizontal and vertical equilibrium (the horizontal pulls are equal and the vertical parts add to the load), the vertical share and the sideways pull on each eyebolt, each tension against the eyebolt's rated vertical load reduced by the share you allow at that leg angle, and the thread engagement as a multiple of the thread diameter against your requirement. Unequal legs show why dividing the load by the number of eyebolts can be unsafe.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Load mass | kg | Mass of the load being lifted, including any attachments. |
| Leg 1 angle from vertical | ° | Angle of the first sling leg from the vertical, measured at the eyebolt. |
| Leg 2 angle from vertical | ° | Angle of the second sling leg from the vertical, measured at the eyebolt. |
| Eyebolt capacity | ||
| Rated vertical working load limit per eyebolt | kg | Working load limit marked on the eyebolt for a straight vertical pull. |
| Share of the rated load allowed at the leg 1 angle | % | Share of the vertical rating the eyebolt maker allows at leg 1's angle, with the eyebolt correctly seated and aligned in the plane of the pull (from the maker's data). |
| Share of the rated load allowed at the leg 2 angle | % | Share of the vertical rating the eyebolt maker allows at leg 2's angle (from the maker's data). |
| Thread | ||
| Eyebolt thread diameter | mm | Nominal diameter of the eyebolt thread. |
| Thread engagement in the load | mm | Length of thread engaged in the tapped hole of the load. |
| Least engagement as a multiple of the thread diameter | Least engagement your practice or the eyebolt maker requires for this load material, as a multiple of the thread diameter. | |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Load mass
- What it is
- The mass of the load hanging from the two eyebolts, including any attachments lifted with it.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1000 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Both leg tensions rise in proportion.
- Get it right
- Use a weighed or calculated mass, not an estimate from the label of a similar item.
What this means: Leg 1 angle from vertical
- What it is
- The angle between the first sling leg and the vertical, measured where the leg meets its eyebolt.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 89°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 45° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The steeper leg (the one nearer vertical) carries more of the load.
- Get it right
- Measure or work it out from the sling length and the eyebolt spacing; uneven slings give unequal angles.
What this means: Leg 2 angle from vertical
- What it is
- The angle between the second sling leg and the vertical, measured where the leg meets its eyebolt.
- Units and format
- Enter a number in °: degrees of angle. The form accepts 0° to 89°. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30° as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The steeper leg (the one nearer vertical) carries more of the load.
- Get it right
- If both legs are equal the split is even; the sling tension tool covers that case.
Eyebolt capacity
What this means: Rated vertical working load limit per eyebolt
- What it is
- The working load limit marked on the eyebolt for a straight vertical pull in line with its shank.
- Units and format
- Enter a number in kg: kilograms. The form accepts 0.000001 kg to 10000000 kg. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1500 kg as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Each eyebolt’s capacity at its angle rises in proportion.
- Get it right
- Read it from the eyebolt’s marking or certificate; an unmarked eyebolt should not be used.
What this means: Share of the rated load allowed at the leg 1 an…
- What it is
- The share of the vertical rating the eyebolt maker allows when pulled at the angle of leg 1, with the eyebolt seated and the eye aligned with the pull.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 55% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Eyebolt 1’s capacity rises in proportion.
- Get it right
- Take it from the maker’s angle table for that eyebolt type; plain eyebolts are often not rated for angled pulls at all.
What this means: Share of the rated load allowed at the leg 2 an…
- What it is
- The share of the vertical rating the eyebolt maker allows when pulled at the angle of leg 2, with the eyebolt seated and the eye aligned with the pull.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 0% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 55% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Eyebolt 2’s capacity rises in proportion.
- Get it right
- Take it from the maker’s angle table for that eyebolt type.
Thread
What this means: Eyebolt thread diameter
- What it is
- The nominal diameter of the eyebolt’s thread, used to express the thread engagement as a multiple of the diameter.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the engagement ratio.
- Get it right
- Use the thread size marked on the eyebolt, such as 20 mm for an M20.
What this means: Thread engagement in the load
- What it is
- The length of eyebolt thread actually engaged in the tapped hole of the load.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer engagement raises the engagement ratio.
- Get it right
- Measure the tapped depth of full thread; a short or damaged tapped hole is a common cause of failure.
What this means: Least engagement as a multiple of the thread di…
- What it is
- The least thread engagement your practice or the eyebolt maker requires for this load material, as a multiple of the thread diameter.
- Units and format
- Enter a plain number with no unit. The form accepts 0 to 10. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.5 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Only moves the engagement pass line.
- Get it right
- Softer materials such as aluminium or cast iron need deeper engagement than steel.
Method and formulas
- Equilibrium of the hook: T₁ sin a₁ = T₂ sin a₂ and T₁ cos a₁ + T₂ cos a₂ = W, giving T₁ = W sin a₂ ÷ sin(a₁ + a₂) and T₂ = W sin a₁ ÷ sin(a₁ + a₂).
- Vertical share T cos a; sideways pull T sin a (equal on both eyebolts).
- Capacity at the angle = rated vertical load × allowed share; compare each leg tension with its capacity.
- Engagement ratio = engaged length ÷ thread diameter, against the requirement.
- Example: legs at 45° and 30° carry 517.64 kg and 732.05 kg of a 1000 kg load, with a sideways pull of 366.03 kg on each eyebolt.
Limitations
- Two legs meeting at one hook, with the load hanging still; dynamic effects of lifting and stopping are not included.
- The allowed share at an angle comes from the eyebolt maker and applies only to eyebolts made for angular loading, fully seated and aligned with the pull.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check eyebolts on a load lifted with unequal sling legs
- Find the tension and sideways pull on each eyebolt
- Check that each eyebolt is engaged deeply enough
Who it is for
- Riggers and lifting supervisors
- Machine designers
- Maintenance engineers
What you get
- Tension in each leg
- Vertical share and sideways pull on each eyebolt
- Each tension against the eyebolt capacity at its angle
- Thread engagement ratio
Interpreting the result
- With unequal legs the steeper leg carries more of the load, so dividing the load by the number of eyebolts understates the heavier one.
- Side pull is what bends and breaks eyebolts; plain eyebolts without a shoulder are for vertical lifts only.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2613–2650, 3450. Topic reference; no source tables or recommended settings are reproduced.
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1536–1537. Topic reference; no source tables or recommended settings are reproduced.
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Open the Eyebolt Lift Check (Unequal Leg Tensions, Angled Capacity, Thread Engagement) calculator