Connecting links—pieces of equipment such as carabiners, snaps or snap hooks, shackles, clevises and quick links that are intended to attach ropes, harnesses, slings or other objects together, or to each other—are used in almost every activity in the tree care industry. This widespread use is an excellent indicator of connecting links’ safety, flexibility and value as tools. However, as with any tool, these links, regardless of their strength, configuration, locking mechanism or material makeup, must be used appropriately to be safe, secure and efficient. The use of an incorrect connecting link, or a correct one used in an inappropriate manner, can result in possible catastrophic failure, injury and even death. Many of the basic guidelines for correct and appropriate use of connecting links in tree care operations can be found in the ANSI Z133.1-2006 Safety Requirements for Arboricultural Operations, but further information and explanation can only improve their safe and appropriate use. The standards and requirements for connecting links for personal or life support are much different from those in non life-support applications, so climbers must not only be aware of those differences, but also apply them properly and consistently in field use.

Personal/life support

Connecting links used for personal or life-support purposes must have a breaking strength of 5,000 pounds. This breaking strength is often expressed in kilonewtons(kN), a metric measurement of force. A breaking strength of 23 kN meets the ANSI requirements for personal support. In addition, personal support connecting links must have various forms of locking mechanisms, depending on the type of connecting link. Carabiners must have a locking mechanism that requires two separate actions for opening and returns to the locked position automatically when released. Manufacturers have developed a variety of carabiners in different shapes and sizes that meet this requirement. In addition, carabiners are significantly weaker when cross or side loaded, so climbing arborists should always ensure they are loaded along the spine or major axis for maximum strength. Snaps or snap hooks need only have a single-action locking mechanism, but users should take care to use the snap appropriately to avoid opening the locking mechanism inadvertently. Connecting links used for personal support should never be used for rigging applications, and vice versa.

Various carabiners of different strengths and materials that were broken through overuse, overloading or side loading. A selection of carabiners in different shapes, sizes, materials and with varying locking mechanisms.


These two connecting links differ in a variety of ways, but of particular importance when used for personal/life support is their difference in construction. The gate of a carabiner is an integral component of its strength, and if the gate is not properly closed and locked, this strength is significantly weakened. The snap or snap hook is typically forged or formed out of a single piece of metal and retains the same strength open or closed. There are hybrid connecting links available that appear to be a cross between a snap and a carabiner. Users should ensure these links interact appropriately with their harnesses and climbing systems on the ground prior to using them aloft.

Non life support

These connecting links would be those used as accessories to attach gear, saws, tag lines, etc., to the climber’s harness; links used in rigging operations; or perhaps connecting links used when establishing mechanical advantage systems in felling/lifting/drifting applications. Although there are no written standards dictating strength or locking requirements for these connecting links, tree care crews should choose carefully from amongst the many choices available to find the appropriate link for their application. For example, a steel, locking carabiner with a breaking strength of 70 kN might be an appropriate choice for attaching a Prusik-minding pulley to an anchor in a mechanical advantage system, but it’s much more connecting link than needed for attaching a handsaw to a harness. Similarly, a lightweight, aluminum, non-locking carabiner might be an excellent choice for hanging a personal first aid kit off a gear loop, but an extremely poor choice for attaching a pulley in a static rigging system.

A variety of snaps/snap hooks manufactured of different materials. Note the lack of a locking mechanism on the spreader snap, making it unsuitable for personal support. Other connecting links that might be used for a variety of climbing and rigging applications.

Dynamic rigging

The use of connecting links in dynamic rigging systems, where sudden violent movements with large shock loads are possible, should be avoided whenever possible. If the dynamic system does require the use of a connecting link, shackles, clevises or other links besides carabiners should be used. The possibility of cross-loading a carabiner during violent movement can lead to catastrophic failure of the carabiner and rigging system. If at all possible, shackles and clevises should be oriented so that running rigging lines cannot loosen their screw-lock mechanisms.

Cycles to failure

Tree care professionals—whether they are using connecting links for life support, rigging or other applications—should always be aware of the concept of cycles to failure. The greater the load experienced by a connecting link in relation to its breaking strength, the weaker it becomes, and the shorter its lifespan. This concept also applies to rigging slings, climbing lines and rigging ropes. For example, a carabiner with a breaking strength of 10,000 pounds is designed to endure that load one time when brand new and correctly used. If the same carabiner is loaded to half its breaking strength, or 5,000 pounds, it will last significantly longer before failure; if it is loaded to 10 percent of its breaking strength, or 1,000 pounds, it will last longer still.

The multitudes of connecting links available make it easy to find one appropriate to the given tree care application, as long as the guidelines of strength, safety and security are followed. The ability to quickly and safely attach and detach items, including oneself, from a variety of systems only increases tree crews’ abilities to accomplish jobs more efficiently. The basic knowledge of connecting links described here will help those crews make appropriate choices and decisions when selecting and employing connecting links in any application.

Michael (House) Tain is a contract climber, splicer, educator and writer currently located in Lancaster, Ky.