Eye bolts, a crucial component in rigging, serve as lifting or securement points. Resembling other rigging hardware like slings, sling hooks, and shackles, they are available in diverse designs and configurations, suitable for rigging, anchoring, pulling, pushing, or hoisting tasks.
Despite their widespread industrial use, eye bolts are often subject to misinterpretation or misuse. Selecting the appropriate type of eye bolt for a specific application, especially when used with other rigging gear, can be a complex task.
This article aims to demystify the various types of eye bolts and their applications, ensuring you avoid incorrect selections that could lead to rigging failures, potentially causing substantial damage or injuries.
Components of an Eye Bolt
Eye bolts come in different designs for specific applications. Familiarize yourself with these terms to understand the various lifting eye bolt types:
- Eye: the loop at the top, which can be bent, welded, or forged
- Shoulder: the “skirt” where the eye and shank meet, designed to resist bending
- Shank: the threaded shaft connecting to the eye
Always ensure the chosen eye bolt meets or surpasses the working load limit for your task and is compatible with the WLL of the slings and other rigging hardware used.
Eye Bolt Markings / Identification
As per ASME B30.26 – Rigging Hardware, each eye bolt must be marked to display:
- Manufacturer’s name or trademark
- Size or rated load
- Grade for alloy eye bolts
Different Types of Eye Bolts
This section introduces terms including shouldered eye bolts, forged eye bolts, nut eye bolts, and machinery eye bolts.
Shouldered Eye Bolts vs. Non-Shouldered Eye Bolts
Selecting the right eye bolt involves determining the need for a shouldered or non-shouldered (plain pattern) eye bolt. Shouldered eye bolts suit vertical in-line lifts and angular lifts. Non-shouldered eye bolts are only for in-line or vertical lifts and must not be used for angular lifts.
- Shouldered Eye Bolts: Designed with a shoulder at the junction of the eye and shank, reducing bending stresses and allowing use in angular lifting if properly seated in the load.
- Non-Shouldered Eye Bolts: Lacking a shoulder, these are suitable only for vertical or in-line lifts and are unsuitable for side loading or angular loading.
Fabrication Processes: Forged vs. Bent Eye Bolts
Eye bolts can be formed by forging or bending a solid rod.
- Forged Eye Bolts: Hammered or pressed into form, altering the metal’s grain structure for increased strength, durability, and suitability for heavier-duty lifting applications.
- Bent Eye Bolts: Formed by bending a solid piece into the eye bolt shape, suitable for lighter-duty applications but not for heavy loads or angular loads.
Nut Eye Bolts vs. Machinery Eye Bolts vs. Screw Eye Bolts
The correct eye bolt type depends on:
- The application or lift nature
- The material or structure for insertion (wood, metal, etc.)
- Load angle: vertical/inline or angular
- Nut Eye Bolts: Fastened with a nut, available in shouldered or non-shouldered forms, and made through forged, welded, or bent eye methods.
- Machinery Eye Bolts: Designed for tapped holes as lifting points, suitable for angular loads up to 45° when shouldered.
- Screw Eye Bolts: Used primarily in light applications and screwed into wood or lag anchors, without a working load limit and not recommended for overhead lifts or heavy loads.
Eye Bolt Materials
Consider the eye bolt material for additional corrosion resistance. Common materials include:
- Stainless Steel Eye Bolts: Maintain corrosion resistance when damaged, suitable for rigorous applications, with 304 being common and 316 grade for saltwater.
- Galvanized Eye Bolts: Protected by a zinc coating against corrosion, suitable for industrial applications where moisture is not a primary concern.
Angular Loading and Rated Capacity
Working Load Limits for eye bolts are based on a straight vertical lift. Angular lifts reduce the WLL and should be minimized. For angular lifts, a properly seated shoulder pattern eye bolt must be used. Loads must always be applied in the plane of the eye, not at an angle. Angular lifts should not exceed a 45°pull.
Consult with the eye bolt manufacturer for WLL adjustments in angular loads.
In selecting the appropriate eye bolt, consider:
- Load weight
- Lift nature
- Insertion material (wood, metal, engineered point, etc.)
- Load angle (vertical/inline or angular)
- Sling angle and type
- Other rigging hardware
Partner with a reputable rigging shop or supplier to determine the best eye bolt type for your application, ensuring design and WLL adequacy for your lifts.
Gulian offers a full inventory of hooks, eye bolts, and other hardware, along with training and certified inspections.
Custom Specifications
Eye bolts can be customized for specific applications, such as adding a cross hole for a bridge pin.
Eye bolts vary in material, predominantly steel and stainless steel, with stainless steel bolts either cast or forged. Other materials include aluminum, bronze, titanium, etc., with finishes like hot-dip galvanizing and plating (zinc or cadmium).
Considerations for Eye Bolts
When ordering, consider the weight, load type, lift angle, and the bolt’s type (forged or formed and bent), material, affixation method, and specifications, including WLL, shank diameter, eye inside diameter, and shank length.
Select and Install Eye Bolts
Choose from regular, shoulder, screw, and machinery eye bolts based on the application. Regular and shoulder bolts are for angular loading, while screw bolts are for wood without a WLL. Machinery eye bolts are designed for angular loading with all holding strength on the threads.
For more information or assistance, consult our Ultimate Guide to Eyebolts or contact us.
Selecting the Right Bolt
Choose eye bolts based on type and capacity, considering plain or regular bolts for vertical loading only and shoulder bolts for vertical or angle loading. Follow the manufacturer’s recommendations for angle loading.
Using Eye Bolts Safely
Ensure proper orientation, packing, and torque of eye bolts. Use one sling leg per eye bolt, inspect and clean threads and holes, and install correctly. Avoid exceeding a 45° horizontal angle and consider a swivel hoist ring for angled lifts.
Avoiding Eye Bolt Misuse
Avoid slings through multiple eye bolts, forcing slings, modifying eye bolts, using bars or wrenches for tightening, painting, forcing hooks or fittings into the eye, shock loading, using a single bolt for rotating loads, worn threads, or inserting hooks in eye bolts. Use a shackle instead.