The Color Code System
ASME B30.9 and the Web Sling & Tie Down Association (WSTDA) established a standardized color-coding system for synthetic web slings that allows riggers to quickly identify sling capacity by color alone. This system applies to polyester flat web slings manufactured to WSTDA-WS-1 standards. While the color code is a quick reference tool, the sling’s identification tag remains the authoritative source for rated capacity.
WSTDA Color Code Chart — Polyester Web Slings
| Sling Color | Width | Ply | Vertical Hitch WLL | Choker Hitch WLL | Basket Hitch WLL (90°) |
|---|---|---|---|---|---|
| Purple | 1″ | 1 | 3,100 lbs | 2,500 lbs | 6,200 lbs |
| Green | 2″ | 1 | 6,400 lbs | 5,100 lbs | 12,800 lbs |
| Yellow | 3″ | 1 | 9,800 lbs | 7,800 lbs | 19,600 lbs |
| Tan/Brown | 4″ | 1 | 12,600 lbs | 10,100 lbs | 25,200 lbs |
| Blue | 5″ | 1 | 16,000 lbs | 12,800 lbs | 32,000 lbs |
| Orange | 6″ | 1 | 19,000 lbs | 15,200 lbs | 38,000 lbs |
Multi-Ply Slings
Web slings can be manufactured with multiple layers (plies) of webbing for increased capacity. The WLL increases proportionally with the number of plies:
| Color | Width | 2-Ply Vertical WLL | 3-Ply Vertical WLL | 4-Ply Vertical WLL |
|---|---|---|---|---|
| Purple | 1″ | 6,200 lbs | 9,300 lbs | 12,400 lbs |
| Green | 2″ | 12,800 lbs | 19,200 lbs | 25,600 lbs |
| Yellow | 3″ | 19,600 lbs | 29,400 lbs | 39,200 lbs |
| Tan | 4″ | 25,200 lbs | 37,800 lbs | 50,400 lbs |
| Blue | 5″ | 32,000 lbs | 48,000 lbs | 64,000 lbs |
| Orange | 6″ | 38,000 lbs | 57,000 lbs | 76,000 lbs |
Identification tip: Multi-ply slings often have the ply count indicated by the number of red stripes woven into the edge of the webbing. One stripe = 1 ply, two stripes = 2 ply, etc.
Hitch Types and Their Effect on Capacity
Vertical Hitch (Straight Pull)
The sling supports the load in a single vertical line. This is the rated capacity — 100% of WLL. Used when the load has a single lift point or when space doesn’t allow for other hitch types.
Choker Hitch
The sling wraps around the load and chokes (constricts) against itself. The choking action reduces capacity to approximately 80% of vertical WLL because the sling is both pulling and bending at the choke point. The actual reduction depends on the choke angle — steeper angles reduce capacity further.
Basket Hitch
The sling passes under the load with both ends attached to the hook. At 90° (vertical legs), the basket hitch doubles the vertical capacity because both legs share the load equally. As the angle decreases, capacity reduces per the sling angle factor.
Angle Factor Application to Basket Hitches
| Basket Angle | Factor | Example: 2″ Green Sling |
|---|---|---|
| 90° (vertical) | 2.0 | 12,800 lbs |
| 60° | 1.73 | 11,072 lbs |
| 45° | 1.41 | 9,024 lbs |
| 30° | 1.0 | 6,400 lbs |
Nylon vs Polyester Web Slings
| Property | Polyester | Nylon |
|---|---|---|
| Stretch at WLL | 3% | 8-10% |
| Wet strength | 100% (no change) | 85-90% (loses 10-15%) |
| Chemical resistance | Poor in alkali (bleach, lye) | Poor in acid |
| UV resistance | Good | Moderate |
| Heat tolerance | Up to 194°F (90°C) | Up to 194°F (90°C) |
| Color code applies? | YES (standard system) | NO (nylon uses its own ratings) |
| Best application | General lifting, outdoor, marine | Shock loading, dynamic lifts |
Important: The WSTDA color code applies specifically to polyester web slings. Nylon slings may use different colors and have different WLL ratings. Always check the sling tag — never rely on color alone.
Sling Identification Tag Requirements
Per ASME B30.9 and OSHA 1926.251, every web sling must have a permanently attached tag showing:
- Manufacturer name or trademark
- Manufacturer code or stock number
- Rated capacity for each hitch type (vertical, choker, basket)
- Sling material (polyester or nylon)
- Number of plies
A sling with a missing or illegible tag must be removed from service immediately. There is no exception to this rule — without a readable tag, there is no way to verify the sling’s rated capacity.
When to Use Which Width
- 1″ Purple: Light loads up to 3,100 lbs. Instruments, small motors, HVAC components.
- 2″ Green: Medium loads up to 6,400 lbs. Engines, pumps, medium machinery. The most common size.
- 3″ Yellow: Heavy loads up to 9,800 lbs. Large motors, transformers, structural steel.
- 4″ Tan: Very heavy loads up to 12,600 lbs. Heavy machinery, large vessels.
- 5-6″ Blue/Orange: Extra-heavy loads. Industrial equipment, precast concrete, heavy fabrications.
Common Mistakes with Web Slings
- Relying on color alone: Color is a quick reference, not a substitute for reading the tag. Multi-ply slings of the same color have different ratings.
- Using a damaged sling “just this once”: A cut, burn, or tear can reduce capacity by 50%+ with no visible warning before failure.
- Exposing to chemicals: Polyester is destroyed by alkali (concrete dust, lye, bleach). Nylon is destroyed by acid (battery acid, muriatic acid). Know your environment.
- Dragging slings on the ground: Grit embeds in the fibers and acts as internal sandpaper, cutting strands from the inside out.
- Not using edge protection: Any load edge with a radius less than the sling width requires corner protection.
Frequently Asked Questions
What do the colors of synthetic round slings indicate?
ASME B30.9 assigns specific colors to indicate rated capacity per eye: Purple is 1 ton (2,600 lbs vertical), Green is 2 tons, Yellow is 3 tons, Tan is 4 tons, Red is 5 tons, White is 6 tons, Blue is 8 tons, and Orange is 10 tons or above. This universal color coding allows riggers to quickly identify sling capacity without reading small print. The system applies only to synthetic round slings, not flat web slings.
Do flat web slings follow the same color code as round slings?
No. Flat web slings (flat eye, twisted eye, and endless types) do not have a standardized color code in ASME B30.9. Manufacturers use various colors for marketing or material identification — green does not mean 2-ton on a flat web sling. Always read the capacity tag attached to the sling. Some manufacturers voluntarily follow the round sling color code for their web slings, but this is not required by any standard.
How do I read the capacity tag on a synthetic sling?
The capacity tag shows: manufacturer name, rated capacity for each hitch type (vertical, choker, basket), sling material (nylon or polyester), length, and width. Nylon tags also show temperature limitations and chemical sensitivities. If the tag mentions ‘polyester,’ the sling resists acids better but is weaker against alkalis. If it says ‘nylon,’ it handles alkalis well but degrades in acidic environments. A missing or illegible tag means the sling must be retired.