The four things that decide whether a lift is safe: the hitch you use, the angle you pull at, the sling you picked, and whether it should still be in service. Written to ASME B30.9 and OSHA 1910.184.
A sling's tag gives you three numbers because the same sling carries a different load depending on how you rig it. Everything below is a multiplier on the sling's rated vertical capacity.
Sling straight up and down between the hook and the load. This is the baseline, the number everything else is derived from.
Sling passed through its own eye and pulled tight. The bend at the choke point costs you capacity, about 25% on wire rope. Chain and synthetic are usually rated at 0.80×. That factor assumes an angle of choke over 120°. A tighter choke derates further; see the table below.
Sling cradles the load with both eyes on the hook. Two legs of support, so twice the vertical rating, but only when both legs run straight up. The moment they splay, the angle table below applies.
The choker factor above is the best case. The sharper the angle the sling doubles back through, the less of that capacity you keep. For wire rope slings ASME B30.9 gives the reduction directly.
| Angle of choke | Percent of choker rated load |
|---|---|
| Over 120° | 100% |
| 90–120° | 87% |
| 60–89° | 74% |
| 30–59° | 62% |
| 0–29° | 49% |
For alloy chain, ASME doesn't publish a table. Rated loads below a 120° choke have to come from the sling manufacturer or a qualified person. Ask us and we'll work it out for the sling you have.
Measure from horizontal. The shallower the angle, the more of the load turns into tension trying to pull the sling apart sideways, and it gets bad faster than most people expect.
| Angle | Capacity factor | Tension per leg on a 10,000 lb load, 2 legs |
|---|---|---|
| 90° | 1.000 | 5,000 lb |
| 60° | 0.866 | 5,774 lb |
| 45° | 0.707 | 7,071 lb |
| 30° | 0.500 | 10,000 lb |
Two things get confused here, and they pull in opposite directions.
What the sling is rated at. A three-leg wire rope bridle carries a higher rating than a two-leg, and a four-leg higher still, so go by the tag. Alloy chain is different: ASME B30.9 caps a quadruple-leg sling at the rated load of a triple-leg, so on chain a four-leg buys you no capacity over a three-leg.
What the load actually does. On a rigid load you cannot assume more than two legs are sharing it evenly. Two legs take the weight and the others steady it, which is why the conservative practice is to calculate a rigid pick on two legs regardless of how many you've hooked up.
Our calculators run these numbers for you, and the sling builder shows rated capacity for every configuration as you spec it.
Most of the time the load tells you which one to reach for. Here is the short version of what each material is good at, and what will ruin it.
Heavy, dirty, general-purpose lifting
Watch for: kinking, crushing on sharp corners, and birdcaging. A kink is permanent damage. It does not straighten out.
Rough service, heat, repeated abuse
Watch for: stretched links, gouges, and heat. Grade 80 and Grade 100 only. Never use proof coil or transport chain for overhead lifting.
Finished surfaces, painted or soft loads
Watch for: cuts, abrasion and chemicals. Always pad sharp edges. A web sling cuts far more easily than it stretches.
Awkward shapes, tight chokes
Watch for: anything that opens the cover. Once the core yarns are exposed you cannot judge what's left. The sling is done.
ASME B30.9 sets three levels of inspection. Only one of them creates paperwork, and all three are your responsibility as the user.
Every new, altered, modified or repaired sling, before it's used. Confirms it's what you ordered, correctly tagged and undamaged. No record required, but note this fires again after any repair, not just on delivery.
Each day or shift the sling is used, by the user or another competent person the employer designates. Satisfies OSHA's "each day before being used" rule. Also required again during use wherever service conditions warrant it. No record required.
Annually in normal service; monthly to quarterly in severe service; for special service, as a qualified person recommends. Written record required: sling ID, service class, date, findings, who inspected, and what happened to it.
These are removal criteria, not judgement calls. If a sling meets any of them it comes out of service. There is no "watch it for a while".
| Sling | Remove from service when you find |
|---|---|
| Wire rope | 10 randomly distributed broken wires in one rope lay, or 5 broken wires in one strand in one rope lay. Cable-laid: 20 broken wires per lay. Braided under 8 parts: 20 per braid; 8 parts or more: 40 per braid. Also: severe localised abrasion or scraping, kinking, crushing, birdcaging, heat damage, corrosion, or cracked, deformed or worn end attachments. |
| Alloy chain | Cracks or breaks. Excessive wear, nicks or gouges. Stretched links or fittings. Bent, twisted or otherwise deformed links or fittings. Evidence of heat damage. Excessive pitting or corrosion. Links or components that no longer hinge freely. |
| Synthetic web | Acid or caustic burns. Melting or charring anywhere on the sling. Holes, tears, cuts or snags. Broken or worn stitching in load-bearing splices. Excessive abrasive wear. Knots in any part of the sling. Discoloration suggesting chemical or UV damage. |
| Round sling | Acid or caustic burns. Evidence of heat damage. Holes, tears, cuts, abrasive wear or snags that expose the core yarns. Broken or damaged core yarns. Weld splatter that exposes the core. Knots anywhere except at the termination. |
| Every sling | A missing or illegible identification tag. No tag, no lift, regardless of what the sling looks like. We can re-tag and re-certify slings we fabricated. |
Every sling we fabricate leaves here tagged. The tag is a legal requirement, not a courtesy, and it's the first thing an inspector looks for.
The two sling types we fabricate have different requirements, and chain's are stricter.
| Wire rope slings | Alloy chain slings |
|---|---|
|
Manufacturer's name or trademark Rated load for at least one hitch type, and the angle it's based on Diameter or size Number of legs, if more than one |
Manufacturer's name or trademark Rated load, and the angle it's based on Nominal chain size Number of legs Grade Length (reach) Individual sling identification: a serial number tying it to its test records |
Send us the load and the pick points. We build wire rope and chain slings in Hatfield, proof test them here, and tag them before they go out.
Removal criteria and inspection intervals on this page follow ASME B30.9 Slings and OSHA 29 CFR 1910.184. This guide is a summary for reference and does not replace the standards themselves or the training your riggers need.