What is an Eye Bolt?
Eye bolts are essential to many wire rope applications as they create an attachment point for wire rope assemblies. They feature a loop at one end and a threaded shaft at the other. The shaft end can be screwed into architecture or an object, allowing wire rope assemblies to be attached. Eye bolts are deployed in various industries, such as lifting, marine, aerospace, engineering, and the military, where their applications include hoisting, rigging, anchoring, pulling, and suspension.
With the vast array of applications for eye bolts across different industries, it’s important to understand the differences between the main types and what they’re used for. This blog will look at the different types of eye bolts and their applications.
Different Types of Eye Bolts
The primary differentiation in eye bolt construction is whether they are forged or formed-and-bent.
- Forged Eye Bolts: These are created by hammering or pressing the formable metal into the loop form of the eye. Forged eye bolts are a stronger and more durable construction capable of withstanding loads up to the tensile strength of the material used. The working load capacity (WLL) of all eye bolts decreases significantly depending on the angle of pull, up to 70% at 45°.
- Formed-and-Bent Eye Bolts: These are made when one end of the solid wire is twisted into a loop and then thread rolled. They are generally only intended for lighter-duty applications as a load over its WLL can twist the bend back, slip out, or snap. Although their strength can be increased by welding the eye closed. Bent eye bolts are typically zinc-plated steel or stainless steel and are usually UNC thread.
When ordering eye bolts, there are several different types to consider depending on their intended application. These include:
Regular (Plain) Pattern Nut Eye Bolt
A regular nut eye bolt is affixed to its load by tightening a nut from the shaft end; this means that there must be relatively easy access from both sides. They can be shoulder or regular (plain) pattern and either forged or formed-and-bent. Nut eye bolts have extended shanks and approximately half the shank is threaded. Nut eye bolts are typically HDG (Hot Dip Galv) finish carbon steel, and are also available in SS (Stainless Steel). Nut eye bolts are typically UNC thread.
Shoulder Pattern Nut Eye Bolt
Usually, with forged eye bolts, the bolt has a skirt or shoulder below the loop to improve its capacity to distribute the load.
Machinery Eye Bolt
These eye bolts are usually forged, shoulder pattern and the fully threaded shank connects into threaded or tapped holes designed as lifting points on equipment. They're available in plain steel, zinc-plated steel, galvanized steel, and stainless steel. The threads are typically UNC or metric. Machinery eye bolts have an oversized eye (relative to nut eye bolts).
Bent-Formed Eye Bolt
These turned eye bolts are designed to be attached to a cable assembly via the eye end or the threaded end.
Lag Eye Bolt
The shank of these eye bolts ends in a screw, specifically for attaching an eye bolt to wood or a lag anchor. They are generally not rated with a working load limit as their strength depends on the type and condition of the wood they are attached to. Short lag eye bolts are called Screw Eye Bolts.
Screw Eye Bolt
These are often formed-and-bent eye bolts for lighter applications. The bolt shank tapers to a screw, allowing it to be affixed to architecture.
Military Spec MS51937
These are domestic machinery eye bolts that are approved for use by all departments and agencies of the Department of Defense. They are made of forged carbon steel and either cadmium plated or uncoated, with diameters dependent on procurement details.
Drop forged from C-1035 steel, heat treated. Available blank or threaded. Self-colored finish is standard; hot galvanized or other finishes supplied on a special basis. Used in lifting applications where larger eyes are required. When ordering prefix stock number with letter "B" (blank) or "T" (threaded) as required. Loads are based on a safety factor of 5 to 1. Working loading limits for lifting eyes are based on a straight vertical lift in a gradually increasing manner, and should never be used for angular lifts.
Eye Bolts with Rings Secured
Ring Bolts are Welded and NOT TO BE USED FOR LIFTING APPLICATIONS.These drop forged ring eye bolts are designed to be attached to a cable assembly via the ring end or the threaded end.
Eye bolts can be engineered with custom features for specific applications. For example, a cross hole could be drilled at the threads' end to install a bridge pin.
As you can see, eye bolts differ in the material used to make them, though the predominant types are steel and stainless steel. Stainless steel eye bolts are either cast or forged. Eye bolts can also be made from aluminum, bronze, titanium, or other materials. There are also a variety of finishes, such as hot-dip galvanizing, and plating (zinc or cadmium).
Considerations for Eye Bolts
When ordering an eye bolt for a particular wire rope assembly, you need to consider the weight, load type, and lift angle. Eye bolts work at their optimum WLL for vertical lifting, and every degree over that decreases rated capacity. The strength of the eye bolt will come down to its type (forged or formed and bent), the metal used, how it is affixed, and specification factors. It's also important to consider the type and angle of the sling or other rigging assembly with which the eye bolt will be used.
Several specification factors must be considered to ensure the eye bolts you order meet your application's requirements. These include:
- Working Load Limit: The maximum weight the eye bolt can safely hold. Forged eye bolts have their size and WLL marked along the eye.
- Shank Diameter: The threaded shank's thickness directly correlates with the WLL of the eye bolt.
- Eye Inside Diameter: The diameter of the loop, which is important depending on the diameter of the wire or hooks/shackles being used.
- Shank Length: How long the threaded shank is.
Eye bolts are wire rope equipment integral to many hoisting, anchoring, rigging, and suspension applications. An eye bolt is created by forming a loop at the end of a threaded shaft, which can be done through forging or bending. Eye loops come in various types depending on requirement but lose much of their rated lifting capacity when moving beyond vertical 0° lifting; in these cases, a shoulder pattern eye bolt should be used.
Other specialty eye bolts exist. Eye bolts are standard right hand thread. For eye & eye turnbuckle applications eye bolts are right hand one side and left hand on the opposite side. An eye bolt where the head is stamped is called a spade bolt. An eye bolt that's matched from bar stock is called a rod end. Eye bolts without threads are called eye rivets. Eye bolts are available in import and domestic origin.
Lexco Cable supplies, installs, inspects, and tests wire rope hardware, including all kinds of eye bolts. In addition, we regularly work with clients to deliver standard specs and custom applications. To find out more about why Lexco is the only source you need for any eye bolt requirements, you can view our catalog or talk to our team.