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Screw-links and strength ratings

Richard Tregoweth - Tuesday, December 08, 2009

Taiwan and China love copying the screw-tight connectors commonly used in climbing. The simplicity and usefulness of a screw-link make them the perfect target. But there is only one original - Maillon Rapides manufactured by Peguet in France - and you will find them at Treetools. Our screw-links have something the imitators don't: certification to European Standards and a guarantee of manufacture under a certified quality system.

Each screw-link is stamped with a rated strength based on its breaking load. Unfortunately, these numbers do cause confusion for many climbers (and arb companies). The number you see relates not only to the screw-link's strength but also its END USE. There are different standards for Industrial Equipment and Personal Protective Equipment (PPE) and European Standards Certification demand different markings for each end use be stamped on the same screw-link.

If the screw-link is destined for PPE use it will be certified to the CE Standards EN 362 (Industrial Falls from Heights) and EN 12275 (Mountaineering and Climbing) and shows a rated breaking strength in kilo Newtons (kN). Under the PPE standards a component must be rated over 22 kN. That means a 6 mm screw-link with a breaking strength of 2000 kg (20 kN) will never meet the PPE standards and therefore cannot be used as part of your PPE gear.

If the screw-link is sold for industrial use it is self certified and stamped with a safe working load limit (WLL) in kilograms (kg). The WLL is defined as a fifth of the breaking strength giving a safety factor of 5. For example, the same 6 mm standard oval screw-link with a 20 kN (2000 kg) nominal breaking strength is stamped with a 400 kg WLL.

Treetools supplies PPE screw-links to the above standards. You will have to decide if you wish to use an industrial screw-link for PPE use. Note: there is no mandatory PPE standard in New Zealand so this decision will need to be made by yourself if you are a recreational tree climber or the safety standards committee if you work for an arb company.

Certification details supplied by Lindsay Main, Aspiring Enterprises

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