Eyebolt Load Capacity and Working Load Limit Guidelines

Eyebolts are widely used as lifting points in material handling, rigging and equipment installation. From construction sites to manufacturing plants, eyebolts provide a simple and reliable method of attaching heavy loads to lifting equipment such as hooks, chains and slings.

Although eye bolts are simple in design, their selection and use must adhere strictly to regulations. One of the most common causes of failure during lifting operations is a misunderstanding of the load-bearing capacity of eye bolts. Typically, the size of the bolt, the lifting angle and the method of installation all directly affect the weight it can safely bear.

This guide will explain in detail the principles behind the load-bearing capacity of eye bolts, the meaning of the Working Load Limit (WLL), and how to correctly select the appropriate lifting eye bolts to ensure the safe conduct of material handling operations.

What is the ‘Working Load Limit’ of an eye bolt?

The Working Load Limit (WLL) refers to the maximum load that a lifting eye bolt is designed to safely bear under normal lifting conditions. Manufacturers determine this value through rigorous testing and apply a safety factor to ensure the reliability of the product’s performance. No matter which type of eye bolts, DIN580 eye bolt or JIS1168 eye bolt, G277 eye bolt, eye bolts have different working load limit.

The rated load value for most lifting eye bolts is stamped directly onto the body of the bolt. This marking allows users to quickly identify the bolt’s safe lifting capacity.

It is crucial to understand the distinction between the Working Load Limit and the breaking strength.

The Working Load Limit (WLL) refers to the maximum safe load that the bolt is permitted to bear during normal operation.

The breaking strength refers to the load value at which the bolt may fail and break.

In most lifting hardware components, the breaking strength is often several times the Working Load Limit. For example, a forged lifting eye bolt may have a safety factor of 4:1 or 5:1. This means that, theoretically, the bolt would only break when subjected to four or five times its rated working load; however, in practical use, it must never be subjected to loads approaching this limit.

Typical Load Capacities for Eye Bolts

The load capacity of eye bolts depend primarily on its diameter and the strength of the material. Generally speaking, larger eye bolts are, higher load capacity will be.

The following table provides general reference data for forged lifting eye bolts commonly used in industrial applications.

These figures are typical industry estimates. Actual load capacity may vary depending on the manufacturer, material grade and applicable standards. Please be sure the technical specifications of the eye bolt before carrying out any lifting operations.

How Lifting Angles Affect the Load Capacity of Eye Bolts

Eye bolts offer maximum strength when the load is applied in a vertical lifting.

When the load is applied at an angle, the distribution of stress on the bolt changes. In this case, the eye bolt no longer bears purely tensile force but begins to bear bending force, which significantly reduces its safe lifting capacity.

In rigging operations, there is a general rule of thumb:

In certain situations involving lateral loading, the actual load-bearing capacity may decrease even further.

For this reason, standard eye bolts should only be used for vertical lifting operations. If angled lifting is absolutely necessary, shoulder eye bolts must be used, and care must be taken to ensure they are installed correctly.

Comparison of Shouldered Eye Bolts and Standard Eye Bolts

There are two main design types of eye bolts used for lifting operations.

• Standard Eye Bolts

Standard eye bolts do not feature a shoulder (flange) beneath the eye. These bolts are designed exclusively for **purely vertical, linear tension**. If lateral loads are applied, the bolt may bend or even fail by breaking.

• Shouldered Eye Bolts

Shouldered eye bolts feature a reinforced shoulder between the eye and the threaded shank. This design enables the bolt to withstand lifting loads at limited angles, provided that the shoulder is in close contact with the mounting surface.

Thanks to this enhanced structural strength, shouldered eye bolts are widely used in industrial lifting and machinery handling operations.

Factors Affecting the Load-Bearing Capacity of Eye Bolts

A variety of conditions may affect the actual lifting capacity of an eye bolt.

1. Thread Engagement Depth

The threaded portion of the bolt must be fully engaged (screwed) into the mounting hole. Insufficient thread engagement depth will result in reduced strength at the lifting point. It is essential to ensure that at least 90% of the threads are engaged.

2. Eye Bolt Material

Most lifting eye bolts are made from forged carbon steel or alloy steel. Compared to bending or welding eye bolts, forged eye bolts are greater strength and more reliable. For heavy-duty lifting operations, forged lifting eye bolts are usually the suggested choice.

3. Mounting Surface

For eye bolts with a shoulder, the shoulder must sit flush against the mounting surface. If there is any gap between the shoulder and the load-bearing surface, bending stresses will be generated during the lifting process.

Washers may sometimes be used to assist with adjustment, ensuring the eye bolt is correctly aligned.

4. Environmental Conditions

In outdoor or corrosive environments, corrosion can weaken the strength of lifting slings over time. In such cases, hot-dip galvanised eye bolts are often selected to enhance their corrosion resistance.

When lifting eye bolts are exposed to harsh environments, regular inspections are particularly important.

Safety Guidelines for Using Eye Bolts

Safe lifting operations begin with thorough planning and the selection of appropriate equipment.

Firstly, ensure that the working load limit (WLL) of the eye bolt exceeds the weight of the object to be lifted. If a multi-point lifting method is used, the distribution of the load must also be fully considered.

Secondly, ensure that the direction of the pulling force aligns with the direction of the eye opening. Applying a lateral load (i.e. where the pulling force deviates from the plane of the eye) can easily cause the bolt to bend or deform.

Thirdly, under normal circumstances, each eye bolt should only be connected to a single sling leg, unless the lifting system has been specifically engineered to permit alternative connection methods.

Conclusion

Selecting the correct lifting eye bolts and strictly adhering to standard lifting operating procedures will help to significantly improve safety levels and operational efficiency in various working environments. If you have any question about working load limit of eye bolts, don’t hesitate to let us know.