Eye Bolt Size and Load Rating Chart: WLL & Weight Ratings Explained

You're rigging a beam lift, hanging a chainfall, or installing a load-bearing anchor point in a shop ceiling. The eye bolt goes in, but the number on the tag — "WLL 1,200 lbs" — means less than you think if the pull isn't perfectly vertical. Most rigging failures happen because someone used the breaking strength number, assumed the angle didn't matter, or used a plain-shank eye bolt where a shouldered one was required.

Here's the chart and the math you need to get it right.

WLL vs Breaking Strength: The Number That Kills People

Every eye bolt tag shows two numbers. The Working Load Limit (WLL) is the maximum load for normal service use. The breaking (or proof) strength is the load at which the bolt fails in a test. These are not the same number, and confusing them is a rigging fatality waiting to happen.

The safety factor on most commercial rigging hardware is 4:1 or 5:1. A bolt rated 2,600 lbs WLL has a breaking strength of approximately 10,400–13,000 lbs. That margin exists because loads in real applications are never perfectly known — dynamic shock loads during a crane lift can momentarily spike to 3–4× the static load. The safety factor absorbs those spikes.

Eye Bolt Load Rating Chart by Diameter

The following ratings are for standard carbon-steel or alloy-steel shoulder eye bolts with a safety factor of 4:1, under a straight (0°) vertical pull. Ratings vary by manufacturer and grade — always verify against the specific product's documentation before use in a safety-critical application.

Angle Derating: The Most Misunderstood Factor

Eye bolt WLL ratings assume the load is applied perfectly in line with the bolt shank — a straight vertical pull. Real-world rigging rarely achieves this. Every degree of angle away from vertical reduces the effective load capacity, and the reduction is steep.

Shoulder vs Plain Eye Bolts: When Each Is Correct

The shoulder — that machined collar just below the eye ring — is not cosmetic. It's a structural feature that transfers angled loads from the threads into the bearing surface against the substrate. Without it, any angled load attempts to bend the threaded shank, and threads have negligible bending resistance.

Use plain (non-shoulder) eye bolts only for: vertical straight pulls where the load direction is fixed and cannot shift. Hanging lights, sign hardware, fixed vertical cable pulls. If there's any possibility of the load swinging, use a shouldered type.

Use shoulder eye bolts for: any application where the load angle may vary, lifting operations, multi-leg sling rigging, or any marine/construction environment. The shoulder must bear fully against the substrate — if you use a washer and the shoulder is floating, you lose the benefit entirely.

Metric eye bolts follow the same principles. An M10 shoulder eye bolt (roughly 0.394" diameter) falls between 5/16" and 3/8" in capacity — approximately 600–800 kg WLL depending on grade. Use the manufacturer's published load table for metric hardware; do not convert imperial WLL ratings directly.

Material: Galvanized vs Stainless vs Plain Steel

Hardware store eye bolts labeled "zinc-plated" or "bright zinc" are for indoor decorative use only. The zinc coating is too thin to provide meaningful corrosion protection, and the base steel is typically low-carbon — not rated for lifting. These are hanging-lamp hardware, not rigging hardware.

Hot-dip galvanized (HDG): Standard for construction rigging, shop lifting, and outdoor applications in non-corrosive environments. Coating thickness of 3–4 mils provides years of outdoor service. HDG eye bolts carry full rated WLL.

Stainless steel (316 grade): Required for marine, coastal, and chemical environments. Note that 316 SS has slightly lower tensile strength than equivalent carbon steel, so a stainless eye bolt may carry a lower WLL than the same-diameter galvanized unit. Always verify the product's specific rating — don't assume same diameter = same WLL between materials.

Alloy steel (quenched & tempered): Specialty eye bolts for maximum WLL in minimum diameter. Used in crane and overhead lifting applications. Usually painted bright colors (green or yellow) to indicate rated hardware. These have WLL ratings 2–3× higher than equivalent-diameter carbon steel hardware.

Installation: Four Points That Determine Actual Capacity

An eye bolt threaded into inadequate substrate is just an ejection mechanism under load. These four factors determine whether the rated WLL is achievable:

1. Thread engagement: Eye bolts need full thread engagement — the full threaded shank length into the receiving material. In wood, you need at minimum 8–10× the bolt diameter of thread penetration. A 1/2" eye bolt needs at least 4–5" of thread into solid wood. Through-bolting with a nut is always stronger than threading into any substrate.

2. Shoulder seating: On shoulder-type eye bolts, the shoulder must bear fully against a flat, solid surface. If the surface is curved, gapped, or if the eye bolt is in a through-hole with a washer that's not matched to the shoulder OD, the angled-load capacity is lost. The shoulder stops where it touches the substrate.

3. Eye orientation: For single-leg slings, the eye opening must be in the same plane as the load direction. An eye bolt rotated 90° to the sling direction applies a twisting, side-loading force the eye is not designed for.

4. Hardware grade: "Eye bolt" at a hardware store means nothing about grade. Look for the WLL stamped on the hardware or a certification to ASME B18.15 (US standard) or DIN 582 (metric standard). Unmarked hardware from non-industrial suppliers has no verified load capacity.

When to Use a Swivel Hoist Ring Instead

If your lift requires the load to rotate, the sling angle will change, or the attachment point must accommodate multi-directional pulls, a swivel hoist ring is the correct hardware. These rotate 360° and pivot 180°, maintaining full WLL rating regardless of load direction. They're more expensive than eye bolts but eliminate the angle-derating calculation entirely.

Common hoist ring sizes (Jergens, Crosby, and similar manufacturers): M8 through M48 metric and 5/16" through 1-1/2" imperial. Rated WLL runs from 500 lbs (5/16") up to 40,000 lbs (1-1/2"). Use them anytime your lift involves swing, rotation, or an attachment point that will see varying load direction.