Can I Join Two Flat Slings Together to Extend the Length?

A rigging crew is preparing a lift. The load is 15 feet long, but the only flat sling available is 10 feet. The supervisor needs a longer sling—and fast. The temptation to simply join two shorter slings together is nearly irresistible.

But the rigging supervisor knows better. According to OSHA 1910.184(c)(2) , whenever any sling is used, slings shall not be shortened with knots or bolts or other makeshift devices. ASME B30.9 similarly requires that slings not be twisted, shortened, lengthened, tied into knots, or joined by knotting.

Lishenflex has been manufacturing synthetic flat slings for decades, and our field experience shows that improper sling connections are a leading cause of rigging incidents. The simple act of tying two slings together can reduce strength by 50% or more, creating a catastrophic failure point under load.

1. Why Joining Slings Directly Is Dangerous

1.1 Knots and Girth Hitches—Severe Strength Reduction

The most common method of joining two slings is a knot or a girth hitch (lark's foot). Both methods create sharp bends that concentrate stress on a small area. According to testing referenced in the UK climbing community, a girth hitch can reduce sling strength by approximately 50%. Even under Lifting Operations and Lifting Equipment Regulations (LOLER), the reduction is at least 20% when done with slings of equal diameter.

SpanSet warns that any type of sling—webbing sling, round sling, wire rope, chain—should not be knotted. Tying a knot will cause the knotted parts to cut into each other and cause damage, which can eventually result in a fatal accident.

1.2 The "Pulley Effect" and Cutting Action

When two slings are joined and placed under load, the connection point acts like a pulley. The slings move against each other under high tension, creating friction and cutting action that can sever fibers. SpanSet explicitly states that knotted slings cause the parts to cut into each other, creating damage that can eventually result in a fatal accident. This is why OSHA and ASME standards prohibit joining by knotting—the damage is progressive and often invisible until failure.

1.3 Industry Standards Prohibit It

Per WAC 296-155-55825, employers must not shorten or lengthen slings by knotting or twisting. This applies to synthetic web slings specifically. Under ASME B30.9, knots in any part of the sling are grounds for immediate removal from service. This means a sling that has been knotted—even once—must be scrapped.

The Mazzella Companies inspection guide lists "knots in any part of the sling" as a condition requiring removal from service, and further states that slings shall not be twisted, tied into knots, or joined by knotting. Similarly, the Lifting Operations and Lifting Equipment Regulations (LOLER) prohibit knotting as a method of shortening or joining slings.

2. What the Standards Say

3. The Right Way to Extend Sling Length

If two flat slings must be joined to achieve the required length, the only safe method is using dedicated lifting hardware.

3.1 Shackles

Shackles are the most common method for joining slings. Each sling's eye is attached to the shackle pin or bow, creating a load-rated connection point. EN 1492-1 specifies that flat woven webbing slings may be used with fittings, provided the fittings are properly rated and compatible with the sling.

Key requirements when using shackles:

• Shackle WLL must equal or exceed the sling's WLL

• Shackle size must fit the sling eyes without binding

• The shackle pin must be properly tightened and secured

3.2 Joker Hooks and Dedicated Connectors

SpanSet recommends the Joker Hook as a safe alternative for extending sling length. The Joker Hook functions as a connecting connector to join two lengths of round slings or webbing slings together, allowing you to create a longer sling when needed. It has lifting capacity, color codes, and complies with EN 1492 standards.

3.3 Soft Connections (When Permitted)

Liftex and other manufacturers allow soft connections only when the connection is made to a properly rated hardware fitting—not directly sling-to-sling. The Chinese standard GB/T 25854 similarly requires that all connecting components be rated and compatible with the sling's WLL, and all parts must be inspected for wear and damage before use.

4. What Happens If You Use a Knotted Sling?

• The sling must be scrapped: Per ASME B30.9, knots require removal from service.

• OSHA citations: OSHA routinely cites employers for using knotted slings. In at least one documented case, a citation was issued for a synthetic web sling that had been tied in a knot.

• Strength reduction: A girth hitch reduces strength by 20-50%, depending on the connection method.

• Catastrophic failure risk: The friction and cutting action at the knot can cause sudden failure under load.

5. Summary and Practical Recommendations

Joining two flat slings by knotting or girth hitching is prohibited by OSHA, ASME, EN 1492-1, and LOLER. The practice reduces sling strength by 20-50%, creates progressive damage from friction, and exposes operators to catastrophic failure risk.

Key takeaways:

1. Never knot or girth-hitch slings together—it is prohibited by multiple standards and reduces strength significantly

2. Use dedicated hardware—shackles, Joker Hooks, or other load-rated connectors are the only safe methods

3. Match ratings—all connecting hardware must have a WLL equal to or greater than the sling's WLL

4. Inspect connections—check that hardware fits the sling eyes and is free from damage

5. Train your team—ensure all riggers know the prohibition on knotted connections

Lishenflex manufactures polyester flat slings to EN 1492-1 and ASME B30.9 standards, with clear color-coded capacity markings and load-bearing stitching. We also offer rigging hardware—including shackles and connectors—designed for safe sling connections.

If you need assistance selecting the right connection hardware for your lifting operations—or need help determining the proper method for extending sling length—please send an email to sales@lishenflex.com, and our technical team will provide one-on-one support.