Slings and hitches
Choke hitch reduced WLL (×0.8)
- where
- choked WLL (t)
- mode factor for the sling arrangement (1 single sling or marked assembly; 1.4 two single slings at 0–45°)
- marked WLL of the sling, straight pull (t)
- utilisation (%)
- load to be lifted (t)
Explain this equation
Gives the reduced rating of a sling used in a choke hitch, wrapped round the load and passed through its own eye. Use it for bundles of tube, pipe or bar where a choke grips the load.
WLL_m is the sling's marked straight-pull WLL. M is 1 for a single sling or a marked multi-leg assembly, or 1.4 when two single slings are used together at up to 45°. The 0.8 is the choke factor. WLL_c is the reduced rating, and U compares your load W with it.
Where the sling passes through the choke it bends sharply and is pinched, which raises the local stress. LEEA applies the same 20% reduction to chain, wire rope, webbing and roundslings.
Sense check: a 2 t sling choked is good for 1.6 t. Two 3 t slings choked at a shallow angle are good for 3.36 t.
Watch out: never force the choke down with a bar or by snatching. Protect slings from sharp edges.
Reduces a sling’s rating when it is used in a choke (noose) hitch around the load. Applies to chain, wire rope, webbing and roundslings.
Enter your values to see the result.
Good to know
LEEA gives the same 0.8 choke factor for chain (BS EN 818-4), wire rope (BS EN 13414-1), webbing (BS EN 1492-1) and roundslings (BS EN 1492-2). For a multi-leg sling, apply 0.8 to the WLL marked for the angle band in use. Two single slings choked at up to 45° to the vertical: 0.8 × 1.4 = 1.12 × the single sling WLL. The reduction allows for the extra stress where the sling bends sharply through the choke.
Common mistake
Pulling the choke tight against the load with a bar or the crane, or choking over a sharp edge. The 0.8 factor assumes the choke settles naturally; forcing it down overloads the eye and the bight.
Limits
Assumes a natural choke angle and no sharp edges (use edge protection). Some manufacturers give further reductions for tight choke angles; their data govern. For planning only: this does not replace a lift plan prepared by a competent person under LOLER 1998 (reg. 8) and BS 7121, and the manufacturer’s WLL markings, load charts and data always govern over this result.
Sources
- LEEA COPSULE Ed. 10, 15.5.2 Wire rope slings (BS EN 13414-1), method of use: choke hitch ×0.8, basket hitch with both ends on the hook 0–45° ×1.4, two single slings 0–45° ×1.4
- LEEA COPSULE Ed. 10, 14.5.2 Chain slings (BS EN 818-4), method of use: choke hitch ×0.8 of the marked SWL, basket hitch 0–45°, legs equally disposed
- LEEA COPSULE Ed. 10, 16.5.2 Flat woven webbing slings (BS EN 1492-1), mode factors: straight 1, choke 0.8, basket parallel 2, basket 0–45° 1.4, 2-leg 0–45° 1.4, 4-leg 0–45° 2.1
- LEEA COPSULE Ed. 10, 17.5.2 Roundslings (BS EN 1492-2), mode factors: straight 1, choked 0.8, basket parallel 2, basket 0–45° 1.4
- The Lifting Operations and Lifting Equipment Regulations 1998 (SI 1998/2307), reg. 8: every lifting operation properly planned by a competent person, appropriately supervised and carried out safely
- HSE L113 Safe use of lifting equipment. Lifting Operations and Lifting Equipment Regulations 1998. Approved Code of Practice and guidance
Results are calculations from the published methods and figures shown, and depend on the data you enter. For planning and checking only. Scaffolds must be erected to NASC TG20 or a bespoke design by competent persons, and lifting operations planned under LOLER by a competent person. Never rely on these results instead of a design, a lift plan or manufacturer ratings.