Key Takeaways
- The hitch configuration you choose changes the rated capacity of the same sling, from 100% in a vertical hitch down to as low as 49% in a low-angle choker.
- Choker hitch capacity percentages differ by sling material: 75% for wire rope and synthetic rope, 80% for alloy chain and synthetic web.
- Basket hitch capacity reaches 200% of vertical WLL only when both legs are truly vertical and the D/d ratio meets ASME B30.9-2021 minimums.
- OSHA 29 CFR 1926.251 and ASME B30.9-2021 both require sling tags to show rated capacity for the hitch type used, and a missing or illegible tag means the sling must be removed from service immediately.
- Always calculate capacity for the actual hitch geometry, including angle of choke and horizontal sling angle, before making a lift.
Sling Hitch Types and Their Effect on Rated Capacity
The sling hitch types you select for a lift directly change the rated capacity of the sling in your hands. A single sling can safely carry vastly different loads depending on whether you rig it in a vertical, choker, or basket configuration. Two standards govern how these capacities are determined and marked: OSHA 29 CFR 1926.251 for construction and ASME B30.9-2021 for sling design, testing, and tagging. American Crane & Safety covers all three hitch types and their capacity effects in its Rigging Courses, available online and on-site.
This article walks through each hitch type, the capacity reduction factors by sling material, the tag requirements under both OSHA and ASME, and a worked example that shows how a single sling’s capacity changes across all three configurations.
Why Hitch Type Changes Sling Capacity
The rated capacity printed on a sling tag is based on a specific hitch configuration, typically the vertical hitch. When you change the hitch, you change the stress distribution on the sling body. A choker hitch introduces a concentration of stress at the choke point. A basket hitch distributes the load across two legs, increasing total capacity.
The tag on every sling must show the rated capacity for the hitch types used. If it does not, or if the tag is missing or illegible, the sling must come out of service immediately. This applies to wire rope, alloy steel chain, and synthetic web slings alike.
Vertical Hitch
The vertical hitch is the baseline configuration. One end of the sling connects to the crane hook or lifting device. The other end connects to the load’s attachment point.
Capacity: 100% of the sling’s rated vertical working load limit (WLL) as shown on the tag.
When to use:
- Loads with dedicated lifting points (shackle holes, engineered lugs)
- Balanced loads where a single attachment point keeps the center of gravity below the hook
Limitations:
- A single vertical leg provides no lateral load control. Always use a tagline.
- Never use a single vertical hitch for loose materials, long loads, or loads with an off-center center of gravity.
Per OSHA’s guidance on safe sling use, the vertical hitch is the simplest configuration, but it requires the load to be stable on its own. If the load can shift, rotate, or slide, a different hitch or a multi-leg sling assembly is the correct choice.
Choker Hitch
The choker hitch wraps the sling around the load and threads one end through the other before connecting to the hook. This gives the sling a grip on the load, which improves control during the lift.
That grip comes at a cost. The choke point creates a sharp bend and concentrates stress, which reduces the sling’s rated capacity.
Choker Capacity by Sling Material
ASME B30.9-2021 assigns different default choker hitch ratings depending on the sling material:
| Sling Material | Choker Hitch Capacity (% of Vertical WLL) |
|---|---|
| Wire rope | 75% |
| Alloy steel chain | 80% |
| Synthetic web | 80% |
| Synthetic rope | 75% |
These percentages apply when the angle of choke is over 120 degrees. As the angle of choke decreases, capacity drops further.
Angle of Choke Reduction
The angle of choke is the angle formed at the point where the sling body contacts itself around the load. ASME B30.9-2021 provides the following reduction factors, consistent across wire rope, synthetic rope, and synthetic web sling chapters:
| Angle of Choke (degrees) | Rated Capacity as % of Choker Rating |
|---|---|
| Over 120° | 100% |
| 90° to 120° | 87% |
| 60° to 89° | 74% |
| 30° to 59° | 62% |
| 0° to 29° | 49% |
This means a wire rope sling in a choker hitch at an angle of choke between 0° and 29° carries only 49% of 75%, or about 36.75% of its vertical WLL. That is a significant reduction that many riggers underestimate.
When to use:
- Round objects such as pipes, poles, and cylindrical vessels
- Bundled materials where grip prevents the bundle from separating
- Loads that require the sling to conform to the shape of the object
Key rules:
- The choke point must always fall on the sling body, never on the eye, fitting, or tag
- A double-wrap choker provides full 360-degree contact and better load control for round objects
Basket Hitch
The basket hitch cradles the load in the sling body, with both ends connecting to the crane hook or lifting device. Because the load weight distributes across two legs of the sling, the capacity increases.
Capacity: Up to 200% of the vertical WLL when both sling legs are truly vertical (90 degrees from horizontal) and the D/d ratio requirements in ASME B30.9-2021 are met.
As the horizontal sling angle decreases from 90 degrees, the capacity drops. OSHA’s sling use tables show the following:
| Horizontal Sling Angle | Basket Hitch Capacity (% of Single Leg Vertical WLL) |
|---|---|
| 90° (vertical legs) | 200% |
| 60° | 170% |
| 45° | 140% |
| 30° | 100% |
Do not use horizontal sling angles below 30 degrees unless the sling manufacturer or a qualified person has specifically approved the configuration.
When to use:
- Balanced, wide, or flat loads
- Loads where the center of gravity is predictable and centered
- Situations where you need capacity above the vertical WLL of a single sling
Key rules:
- The load must be balanced and stable in the basket. If it can roll or shift, add a second wrap or use a different hitch.
- For wire rope slings, the D/d ratio (diameter of the load contact surface divided by the rope diameter) should meet the 25:1 ratio specified in ASME B30.9-2021 for full rated capacity. Synthetic rope slings require a minimum D/d ratio of 8:1.
Capacity Comparison: All Three Hitches at a Glance
| Hitch Type | Capacity (% of Vertical WLL) | Best Used For | Key Limitation |
|---|---|---|---|
| Vertical | 100% | Loads with fixed lifting points | No lateral load control without a tagline |
| Choker (over 120°) | 75% (wire rope/synthetic rope) or 80% (chain/synthetic web) | Round objects, bundled materials | Capacity drops sharply at lower choke angles |
| Basket (90° legs) | 200% | Balanced, wide, or flat loads | Requires both legs vertical and proper D/d ratio |
Sling Material Considerations: Wire Rope, Chain, and Synthetic Web
The type of rigging material you select affects not only the hitch capacity percentages but also the temperature limits, durability, and design factor for the lift.
| Property | Wire Rope | Alloy Steel Chain (Grade 80/100) | Synthetic Web |
|---|---|---|---|
| Design factor | 5:1 | 4:1 | 5:1 |
| Choker capacity (% of vertical) | 75% | 80% | 80% |
| Max temperature | 400°F (non-fiber core); remove fiber core above 200°F | Up to 1,000°F with derating per OSHA tables | Nylon/polyester: 180°F; polypropylene: 200°F |
| Advantages | Strong, abrasion resistant, good cost-to-strength ratio | Abrasion resistant, repairable, adjustable, handles high heat | Lightweight, flexible, protects finished surfaces |
| Disadvantages | Heavy, can kink, internal corrosion risk | Heavy, can damage finished surfaces | Susceptible to cuts, abrasion, UV degradation |
Temperature limits come from OSHA 1926.251: synthetic web slings made of nylon or polyester must not be used above 180°F (82.2°C), polypropylene must not be used above 200°F (93.33°C), and fiber core wire rope slings must be permanently removed from service if exposed to temperatures above 200°F (93.33°C).
When to Choose Each Material
- Wire rope: Structural steel erection, general construction lifts, abrasive environments
- Alloy steel chain: High-temperature applications, repeated use on rough surfaces, adjustable multi-leg configurations
- Synthetic web slings: Finished surfaces, entertainment rigging loads, lightweight equipment, situations where sling weight matters. AMC&S covers proper sling selection in its Entertainment Rigging Courses for crews working in live event production.
Chemical exposure matters too. Nylon degrades when exposed to acids. Polyester degrades when exposed to alkalis. Check the sling manufacturer’s data for chemical compatibility before rigging and slinging in any environment with chemical exposure.
Worked Capacity Example
Sling: 2-inch wide, single-ply polyester web sling rated at 3,200 lbs vertical WLL.
Load: 2,400 lbs.
Here is how the sling capacity changes across each hitch type:
1. Vertical hitch
– Capacity: 100% of 3,200 = 3,200 lbs
– 2,400 lb load is within capacity. Lift is acceptable.
2. Choker hitch, angle of choke over 120°
– Synthetic web choker factor: 80%
– Capacity: 80% of 3,200 = 2,560 lbs
– 2,400 lb load is within capacity, but with only 160 lbs of margin.
3. Choker hitch, angle of choke between 90° and 120°
– Choker factor: 80%
– Angle of choke reduction: 87%
– Capacity: 3,200 x 0.80 x 0.87 = 2,227 lbs
– 2,400 lb load exceeds capacity. You need a higher-rated sling for this configuration.
4. Basket hitch, legs vertical (90° horizontal angle)
– Capacity: 200% of 3,200 = 6,400 lbs
– 2,400 lb load is well within capacity.
5. Basket hitch, 60° horizontal angle
– Capacity: 170% of 3,200 = 5,440 lbs
– Still within capacity.
6. Basket hitch, 45° horizontal angle
– Capacity: 140% of 3,200 = 4,480 lbs
– Still within capacity.
The takeaway: the same 3,200 lb sling can carry anywhere from 2,227 lbs to 6,400 lbs depending on the hitch type and geometry. A choker hitch at a moderate choke angle made this sling inadequate for a 2,400 lb load, while a basket hitch gave more than double the needed capacity. Always calculate before you lift.
Capacity Tag Rules: OSHA 1926.251 and ASME B30.9-2021
Both OSHA and ASME require sling tags to display specific information. Here is what each standard requires, broken out by sling type.
OSHA 1926.251 Tag Requirements
- All slings (§1926.251(a)(2)(i)): Permanently affixed, legible identification markings as prescribed by the manufacturer, stating recommended safe working load
- Wire rope slings (§1926.251(c)(16)): Size, rated capacity for hitch type(s) used and the angle basis, number of legs
- Synthetic web slings (§1926.251(e)(1)): Manufacturer name or trademark, rated capacities by hitch type, material type
- Alloy steel chain slings (§1926.251(b)(1)): Size, grade, rated capacity, sling manufacturer
ASME B30.9-2021 Tag Requirements
- Wire rope: Manufacturer name/trademark, rated load for at least one hitch type and its angle basis, diameter or size, number of legs
- Synthetic web: Manufacturer name/trademark, manufacturer code or stock number, rated load for at least one hitch type and its angle basis, type of synthetic web material, number of legs
- Alloy chain: Manufacturer name/trademark, grade, nominal chain size, length, number of legs, rated load for at least one hitch type and its angle basis, serial number
If the tag is missing, damaged, or illegible, the sling must be removed from service immediately. No tag means no lift.
Pre-Use Inspection
Per OSHA 29 CFR 1926.251(a)(1), a competent person designated by the employer must inspect every sling and all fastenings and attachments each day before use. Additional inspections are required during use when service conditions warrant it. Any damaged or defective sling must be removed from service immediately.
ASME B30.9-2021 adds a requirement for periodic documented inspections at intervals not exceeding 12 months for normal service conditions, with more frequent inspections for severe service.
For a quick field reference on sling inspection criteria and capacity tables, download the AMC&S Rigging Pocket Guide (English) or the Rigging Pocket Guide (Spanish).
Training for Riggers and Supervisors
Understanding sling hitch types, capacity calculations, and inspection requirements is foundational knowledge for every rigger and rigging supervisor. If your crew needs formal training on these topics, American Crane & Safety offers several options:
- Rigging Courses: Available through the online course catalog for self-paced study
- On-site training: AMC&S instructors come to your location and train your full crew. Request on-site training here.
- NCCCO Prep Course: For riggers pursuing NCCCO Rigger Level 1 certification, AMC&S offers an online NCCCO Prep Course
- State-specific training: Find rigger training and NCCCO prep by state
OSHA can issue citations when slings are used without proper capacity knowledge or when workers lack adequate training. Penalty amounts are adjusted annually. See OSHA’s penalties page for current figures.
Getting your crew trained before a project deadline or an audit is easier with both online and on-site options available. Review the full course catalog or contact AMC&S for on-site scheduling.
Frequently Asked Questions (FAQ)
What is the capacity of a choker hitch compared to a vertical hitch?
It depends on the sling material. Wire rope and synthetic rope choker hitches are rated at 75% of the vertical WLL. Alloy steel chain and synthetic web choker hitches are rated at 80% of the vertical WLL. These percentages drop further as the angle of choke decreases below 120 degrees.
When does a basket hitch provide 200% of the sling’s rated capacity?
A basket hitch reaches 200% of vertical WLL only when both sling legs are truly vertical (90 degrees from horizontal) and the D/d ratio meets the minimums specified in ASME B30.9-2021. As the horizontal sling angle decreases, capacity drops.
What must be on a sling tag per OSHA 1926.251?
The tag must show identification markings prescribed by the manufacturer, including rated capacity for the hitch type used. Wire rope sling tags must also show size, angle basis, and number of legs. Synthetic web sling tags must show manufacturer name, rated capacities by hitch type, and material type.
Can I use a sling if the capacity tag is missing or unreadable?
No. Both OSHA 29 CFR 1926.251 and ASME B30.9-2021 require legible identification. If the tag is missing or illegible, the sling must be removed from service immediately.
Where can I get rigging training that covers sling hitch types and capacity calculations?
American Crane & Safety offers Rigging Courses online through their course catalog and on-site at your location. They also provide a free Rigging Pocket Guide in English and Spanish for quick field reference.