13.1 Eyebolts, Shoulder Seating and Angular Demand
Key Takeaways
Do not loosen an eyebolt simply to orient its eye.
Required engagement and shoulder seating are product specific.
Apply angular reductions to the actual leg tension, not just vertical weight share.
Identify the lifting point and mounting structure
An eyebolt provides an eye attached to a threaded shank. Its allowable load depends on product type, size, mounting material, engagement, installation and pull direction. An ordinary hardware-store eye or an unmarked bolt cannot be treated as a rated lifting point by appearance.
A plain or unshouldered eyebolt is generally restricted to its specified in-line loading. A shouldered eyebolt can permit angular loading under its manufacturer’s conditions, commonly with substantial reductions. Neither type accepts an arbitrary sideways pull through the eye. Read the product’s permitted direction and angle definition.
The object’s tapped hole is part of the load path. Its material, depth, thread condition and location must support the planned force. An adequately rated eyebolt in a thin, damaged or unapproved hole does not establish a sound attachment. Manufacturer installation requirements and the load’s handling approval must both be satisfied.
Seat the shoulder correctly
Where required, the shoulder must bear fully on a suitable flat surface. A gap, counterbore or uneven mounting face can introduce bending. Align the eye with the permitted pull plane using the manufacturer’s approved procedure. Do not back the eyebolt out merely to obtain convenient orientation.
Washers or shims may be permitted for particular products, but there is no universal allowance of “one thread pitch” for every eyebolt. Use the specified type, number and arrangement, maintaining required engagement and shoulder contact. Improvised stacks can change how the force enters the shank.
| Installation check | Reason |
|---|---|
| Correct product and thread | Prevents an unqualified or mismatched attachment |
| Suitable mounting material | Establishes force transfer into the load |
| Required engagement | Avoids inadequate thread capacity |
| Shoulder seating | Preserves the approved bearing condition |
| Eye alignment | Prevents an unapproved out-of-plane pull |
A shank bottoming in a blind hole can create a false impression of tightening while leaving the shoulder unsupported. Check the actual hole depth and engagement. Debris and damaged threads can produce the same false resistance. Additional wrench force is not a substitute for a suitable mounting condition.
Apply angular rating and sling demand separately
The sling angle determines demanded tension, while the eyebolt manufacturer’s angular rating determines available capacity. These are distinct operations. A 50% vertical share does not mean the eyebolt can be rated for half the payload without the sling-angle and mounting-direction checks.
For a training problem, assume a supplied shouldered eyebolt has 10,000-lb in-line WLL and a permitted 45-degree pull from its axis at 30% rating. Its available capacity in that stated condition is 3,000 lb. If actual inclined leg tension is 3,500 lb, the connection fails the numerical check. The 10,000-lb in-line rating cannot be used for the angular condition.
Do not apply the supplied 30% value to every eyebolt or every angle between zero and 45 degrees. Different products and angle definitions can have different tables. Manufacturer permission for one angular plane does not authorize perpendicular loading across the eye.
Avoid the common two-leg trap
Consider a balanced 8,000-lb load with two slings at 45 degrees from horizontal. Each vertical share is 4,000 lb, but each leg tension is approximately 5,657 lb. If the supplied angular eyebolt rating is only 3,000 lb, selecting two eyebolts does not make the system adequate. Both connections exceed their applicable limit.
The load’s lug or tapped structure must also be approved for the force direction. An eyebolt table cannot establish the strength of an unknown cast housing. If angular lifting is unsuitable, an approved hoist ring or redesigned attachment method may be appropriate, subject to its own installation and rating requirements.
Inspect and remove unsuitable points
Check identification, cracks, wear, bent shanks or eyes, damaged threads, corrosion and heat damage under the applicable criteria. A bent eye is not acceptable up to an invented ten-degree allowance. Do not straighten it or chase severely damaged threads to make installation possible.
Inspect the mounting area for cracking, thread damage and unsuitable contact. Remove or stop use when the required condition cannot be established. Replacing the eyebolt alone will not resolve a damaged hole or weakened surrounding material.
Field scenario
The eye points across the intended sling plane after its shoulder seats. The crew proposes loosening it half a turn. That creates an unsupported shoulder and may violate installation instructions. Use the manufacturer’s approved orientation method or a compatible lifting point, and confirm engagement and force direction. Do not let convenience override the mounting condition.
Keep threaded points protected when stored, and avoid damage to the eye or shank during removal. If lifting points remain installed after placement, follow the load manufacturer’s instructions for their subsequent use or protection. A point intended for a previous component configuration should not be assumed to rate the newly assembled system.
Sources: CCO eyebolt and hardware references, Crosby lifting-point instructions.
A supplied eyebolt has 10,000-lb in-line WLL and 30% permitted angular rating for the stated condition. What angular capacity applies?
3,000 lb
10,000 lb
7,000 lb
33,333 lb
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