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Tree Climbing Gear Glossary

Tree climbing and arborist work are fields which have their own jargon and technical terms. Books, catalogs, and web sites having to do with tree climbing and tree climbing gear will use many terms and abbreviations, the most common of which we will define here. These definitions are not meant to provide instruction in any way, but merely to be used as a reference. If there are terms you would like to see added here, please contact WesSpur.


Average Breaking Strength. Some manufacturers of rope or hardware supply an Average Breaking Strength (ABS) for their products, which is the average applied force at which the rope or device fails. Factors such as shock loading will exert many times the weight of the load in force on the tree gear in question. If you know the Average Breaking Strength for the gear in your system, you can calculate a Working Load Limit (WLL) appropriate for your gear.

Example: Samson Stable Braid 1/2" Rope has an average breaking strength of 10,400 lb.

Average Breaking Strength

See the definition for ABS above.

Bend Radius

Bend radius in rope refers to the bend formed in a line when it passes around any object; a branch, through rings in a friction saver, or the sheave of a block or pulley. Any bend in a line compromises the strength of the rope to a degree, due to the way part of the rope fibers in the line are compressed and therefore unable to do work in supporting the load. A bend radius of 4 to 1 is recommended as a general ground rule, although twice as wide (an 8 to 1) is ideal. An exception to this rule exists in regards to twisted ropes due to their construction, where a bend radius of 10 to 1 is required for optimal strength retention.

Cambium Saver

See the definition for Friction Saver below.


A designation specific to Samson Rope, which differentiates rope on the basis of material. Class I ropes are those made with Polyester, Olefin, or Nylon. Class II ropes are those that contain high modulus fibers such as Dyneema, Vectran, Technora, and/or Zylon. A rope cannot be both class I and II, and as such the use of high modulus fiber in a rope, even if it is primarily made of Class I material, will usually designate it as Class II; this is true only if the high modulus fibers impart strength and/or stretch characteristics to the rope as a whole.

Compounding of Forces at the Rigging Point

This term describes the doubling of force exerted on the suspension point in a rigging or climbing system (tree limb, block, etc.) when a load is suspended on a rope running over a suspension point. An equal amount of force must be applied to the other end of the rope to keep the load from moving. The suspension point carries double the weight of the load on one end of the rope. This applies to rigging systems and also SRT climbing systems.


This is the abbreviation for Doubled Rope Technique, and describes a climbing system where the climber's line is doubled by passing through a friction saver and back down to the climber. The doubling of the rope means the climber must move 2 feet of rope through the system for each foot of elevation gained, and gains mechanical advantage.

Dyneema (UHMWPE/Spectra)

An extremely strong form of polyolefin made from long chains of polyethylene. Excellent tensile strength mixes with an incredibly low elasticity.

AmSteel-Blue is a high-strength, cable-replacing rope made with Dyneema fibers.


The degree to which a rope will elongate when force is applied to it. The elasticity of a rope is often given as a percentage increase for a given amount of force.

Example: Teufelberger's Tachyon will elongate roughly 2.2% at 10% of its ABS (710 lb of force).

False Crotch

A suspension point in a tree other than a natural crotch created with the use of slings, pulleys, friction savers or other devices. The use of a false crotch has advantages for both tree rigging and tree climbing systems. False crotches can be installed on any structurally sound portion of the tree, freeing the tree climber from being dependent on the natural limbs or crotches of the tree for use as the suspension point. Running climbing or rigging ropes through hardware protects both the rope and tree. The use of a false crotch is necessary in negative blocking.

Example image of a negative blocking system using a false crotch.

Example image of a false crotch for a climbing system.


A flipline is a type of work positioning safety lanyard which gets its name from the way it is "flipped" up the tree while spur climbing. Sometimes also called a "scare strap" or "safety". Fliplines are used to secure the climber to the trunk of the tree while climbing with spurs. Fliplines may have a wire-core for added protection from a chainsaw. ANSI standards for safety in arboriculture require the use of two connections to the tree while cutting, of which a flipline is often one.

Example picture of climbing with a Wire-core flipline.

Friction Saver

Also called Cambium Savers or Rope Savers. The Friction Saver is a device which wraps around the limb or crotch in the tree where a rope will run. The rope then runs either through rings at the end of the friction saver, or through the center of the rope saver depending on the style of device. This protects the rope from abrasion and also protects the tree from the friction of the running rope. Friction savers are used to create a false crotch in tree climbing.

Example image of an adjustable friction saver.

Example of a cambium saver.


Minimum Break Strength, generally speaking, is a number that represents 3 standard deviations from the ABS in a normal distribution. This ensures that 99.73% of ropes will break above the MBS and eliminates the danger of outliers.

Natural Crotch

Natural Crotch is the term used for the crotches in trees where branches meet the trunk. These can be useful places to install a climbing or rigging line, though both the rope and tree will experience more abrasion and wear, and they may not be located in ideal places. Compare to to a False Crotch.

Negative Blocking

This term is used to describe rigging in which the arborist block is installed below the trunk or limb to be removed, such as in butt-hitching during removals.

Rope Saver

See the definition for Friction Saver above.

Shock Loading

Shock loading is the term used when a rope system or rigging device has a sudden load applied to it, usually by catching a falling object. When a device is shock loaded, a much greater force is applied to it than the weight of the object being caught. The farther the object falls, the greater the force applied. This force is many times the weight of the object. This is why it is important to stay within the Working Load Limit of the tree equipment being used.

Climbing gear which has been shock-loaded should be retired from use.

Example: Butt hitching is an application where the rigging system will experience shock loading.


SRT stands for Single Rope Technique and describes a rope climbing system in which the climber ascends a single leg of the rope, while the other leg is anchored.


Spurs is one of the most common terms for the spiked climbing tools worn on the leg by tree or pole climbers. Also sometimes called "Climbers", "Hooks", "Gaffs", "Irons", or "spikes". Tree climbing spurs are typically fastened at the ankle with a synthetic strap and around the calf with a second strap which runs through a pad. "Gaff" is the appropriate term for the spike portion of the climbing spur. A set of climbing spurs is used with a tree climbing harness and a flipline.

Example picture of a Buckingham steel climbing spur with T Pad.


In the context of a ropes construction, "strand" refers to the number of strands that make up the rope. A 3 strand rope, for example, is made up of three distinct strands that are twisted together to form one larger rope. The strand count can vary within one rope if it has a distinct core and cover; for example, a 24 strand jacket can cover a 12 strand core.


An aramid fiber with extremely high heat resistance and no melting point (it instead disintegrates at 930F). The critical temperature (working heat limit for rope) is an incredible 520 degrees Fahrenheit!


High strength and heat resistant synthetic fiber, favored for its high melting point of 625 degrees Fahrenheit. Vectran frequently sees applications in rope construction, sails, and various Aerospace projects, among other uses.


Working Load Limit. See Working Load Limit below.

Working Load Limit

Working Load Limit (WLL) is the maximum weight that the product is intended to handle safely. This is a percentage of the product's Average or Max Breaking Strength. The ANSI Z133 standards for arboriculture outline Working Load Limits at 10% of ABS for Textile products and 20% for hardware.

Example: An arborist block with 40,000 lb. breaking strength will have a working load limit of 8,000 lb. at 20% of the breaking strength.

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