BLOCKS VS. PULLEYS

There are dozens of pulleys and blocks available for the use of arborists today. However not all are created to the same specifications, and there are many applications which will put high demand on the hardware and for which only certain blocks should be used. While the terms "block" and "pulley" are largely interchangeable, we have divided them into two main groups for clarity:

• Blocks
  
  Built for tree rigging, including negative blocking - sustain shock loading a situation where the load free-falls momentarily before being caught by the block. This places far more force on the hardware than normal lowering, therefore only arborist blocks should be used in such situations. Arborist blocks have widened cheek plates to protect the rigging line from abrasion against the tree. Arborist blocks also have an upper sheave to safely attach a rigging sling.
  
  See our collection of Blocks Here.
  
  
• Pulleys
  
  Built for many purposes, not ideal for negative blocking - excellent tools for lowering static loads. They are not manufactured to handle shock loading and for these reason are often cheaper than arborist blocks. The relatively narrow cheek plates on a pulley may expose the rope to abrasion, so care should be taking that the line does not rub against the tree when rigging with a pulley. Most pulleys have carabiner holes in the upper body rather than an upper sheave, and so the rigging sling can not be tied directly to the pulley, and a shackle or clevis is necessary for safe operation.
  
  See our collection of Pulleys Here. 

Factors to consider when choosing a block or pulley are:

• Rope Diameter Capacity - Blocks may be safely used with rope sizes up to the max. diameter capacity.
• Sheave Diameter - The wider the sheave diameter, the less it will reduce the breaking strength of the rope or sling.
• Working Load Limit (WLL) - Working Load Limit is the maximum load the block is intended to handle. The percentage of breaking strength that constitutes the WLL is different from one manufacturer to another, but is generally 20 -25%.
• Breaking Strength (Brk Str) - This is the weight at which the device fails under test conditions.
• Bearing vs. Bushing - Bearings are more expensive than bushings, but are more efficient and are sealed against dirt and sawdust. In practical terms, they have identical strength properties.

Carabiners

Carabiners come in a variety of shapes, sizes, and strengths and can be used for years if they are not damaged by a serious blow or long fall (hairline fractures can develop in aluminum carabiners after a fall). You’d be surprised how much of a beating a carabiner can take. We’ve seen people with 30-year-old carabiners still looking untouched – though we wouldn’t recommend this. Inspect all carabiners frequently. 

Carabiners used in life-support applications shall be of the selfclosing, positive-locking type, (triple action, double auto-locking, three-stage) and along with screw links, shall have a minimum tensile strength of 5,000 pounds (22 kN). Several types of steel and aluminum carabiners meet these requirements. Standard one-quarterturn, twistlock carabiners do not have a positive-locking mechanism and shall not be used in lifesupport applications.

Carabiners sold for climbing must have passed at least one of two sets of safety standards, and show the relevant marks. The first is the EN 12275:2013 rating and a CE marking, with a code for the lab that produced the test. Carabiners can also be certified by the UIAA and show their mark.

The UIAA certifications are based on the CE ones so they should be roughly the same minimum standards, with some extra conditions. Most carabiners are rated to both the UIAA and CE standards, so show both markings. If your carabiner doesn’t have at least one of these, don’t use it for climbing.

The full UIAA specifications for carabiner strength can be viewed here (if you’re into that kind of thing).

The minimum strength for most carabiners rated for climbing is 20kN on the major axis. Carabiner strength is rated in kilonewtons (kN) as it’s a measure of force, not weight. A kilonewton is the equivalent of 225lbs of force. Keep in mind that the weight ratings are NOT the lowest strength that a carabiner broke at in testing, but found using a statistical average. That means even if a carabiner is marked at 21kN of breaking strength – it could fail at a lower load. That being said, the vast majority of carabiners will break at a higher kN value than the minimum printed on the carabiner in normal situations.

If carabiners are loaded incorrectly, they can break at much less force than rated for. Avoid these situations whenever you can. Most of the time we see carabiners break, it’s from the nose hooking on a bolt.

• Cross loaded – When a carabiner is being pulled on its minor axis (from side to side) it is at its weakest. Avoid this by keeping an eye out when you are belaying and climbing, or buy a special belay carabiner that won’t cross-load
• Nose hooking – This happens when you clip just the nose of a carabiner into something, leaving the gate open and the nose snagged. This commonly happens when clipping a quickdraw into a bolt in sport climbing. This is very bad – carabiners will break easily if loaded like this.
• Multi-Directional Loading – Most climbing carabiners are designed to be pulled in two directions, not three or more. Strength is lost when used like this to various degrees. Try to avoid
• Cantilever Loading – This often happens accidentally with quickdraws in bolts. Falls can (and have) resulted in the carabiner breaking.
• Loading Over An Edge – This can happen outdoors on badly placed bolts or with trad gear that should be extended with an extra sling. This can result in just 30% of the rated strength!

Steel carabiners are heavier than aluminum carabiners and will usually have a greater breaking strength. While the extra weight can be a disadvantage when carrying equipment into the tree, the steel carabiner is stronger.

A carabiner with a large gate opening is recommended for any rescue situation. Carabiners shall not be painted or covered with tape (other than a small piece for identification) because the covering may mask fractures or other defects.

Carry plenty of carabiners into the tree or have them available on the ground. When attaching a carabiner, always make sure it is properly attached, it is loaded only through the long axis, and its gate is closed and locked. Never place a load on the gate of a carabiner. Screwlock carabiners can be used only in applications that do not involve life support. When using these carabiners, don’t overtighten the locking mechanism or tighten it when the carabiner is under load; doing so may cause the locking mechanism to jam.

Use compressed air to remove grit and use non-abrasive hand cleaner to remove sap. Thoroughly rinse and dry. Use graphite to lubricate components. Never use oil because it will attract dust.

A minimum of 4, triple-action, double-locking life support style, and at least 2 standard ovals or Ds for gear attachment and other miscellaneous, non-life supporting uses

Screw Links

Like carabiners, screw links are a strong, secure means of attachment and can be used instead of knots. They have a threaded sleeve closure instead of a springloaded hinged gate.

Screw links can withstand multidirectional forces placed on them while carabiners are only designed to be loaded along their long axis.

Consider using screw links when a semipermanent attachment is needed (such as chicken loops) or to attach tie-in points on a chest or seat harness.

Do not overtighten the gate screw. When screw links have been under a heavy load, you often need pliers to loosen the threaded sleeve.

WHEN TO REPLACE CARABINERS & SCREW LINKS

The best way to find out if a carabiner should be replaced is with a visual check. Age comes into play, but the major factors in replacing a carabiner are normally obvious when looking at them closely. If you see any of these signs on a carabiner you should immediately replace it:

• Rust - Any rust on the outside of the carabiner means the inner metal has probably been weakened.
• Burrs or sharp edges where a rope can run through. It’s normal to have small burrs on the bolt side carabiner of quickdraws, but burrs and sharp parts on the carabiner where the rope runs through are bad. Ropes can cut pretty easily when running over a sharp edge on a biner.
• Large Grooves - Where a rope runs over the same areas consistently, a groove forms. When this goes past a millimeter or so, sharp edges form on the side of a groove. These can easily cut a rope in a fall.
• Gate won’t close - A sticky gate can often be cleaned but one that doesn’t snap close should be retired straight away.
• Cracks - Any cracks mean a carabiner should be replaced. Cracks generally form in areas around holes like where the rivet pin is, or near to the edges of the main body like at the nose.
• Bent - If your carabiner has suffered a bend that wasn’t there before, its structure will have been significantly weakened and should not be climbed on again.
• Loose / Damaged Rivet - Any risk of the carabiner not closing is a major problem.
• Missing Parts – Some carabiner gates have a few small parts that help the spring function. If one of these falls out, it could stop closing.
• Sea Water Damage - Anything that looks like “pitting”, or a mottled discoloring of metal means serious damage. Flaking or peeling will eventually occur. These can break with hand strength only.
• Fire Damaged - If one has been in or near a fire, it could look fine but the carabiner strength can be comprised by internal damage. Aluminum and steel don’t need to melt to be massively weakened.

• If a carabiner has been stored or left near certain corrosive chemicals, you should also seriously consider replacing them. Car battery acid from leaving biners on the floor of a car, leaving them near spilled cleaning chemicals, and climbing on the coast near to the sea are three common situations.

What should be ok:

• Falls - Carabiners are designed to be loaded and fallen on. Whether it’s the biner on your cam, quickdraws, or anchor, they can take repeated falls.
• Drops - You don’t need to replace carabiners that are dropped, but it depends on what you think is safe. A drop from a few meters up might be OK, but higher than that introduces the risk of internal fractures. Any visible cracks are serious problems.
• Worn Anodizing - The color of carabiners comes from anodizing, a chemical process that turns the outer of a biner into a form of coating and coloring all in one. This anodized color can wear without any major problems – though opens it up to the elements easier.
• Slight Wear - Some scuffing and wear are OK for carabiner strength.
• Small Groove - A slight groove is the most common thing that climbers will ask about when thinking about replacing a carabiner. It depends on the design of the biner. Most manufacturers recommend replacing when the groove is 1mm or more, which is a good rule of thumb.

4 CARABINER SHAPES

It's important to determine which carabiner shape is most ideal for your own use case. Use the info below to help you decide:

"D"-SHAPED CARABINERS

Regardless of the oval carabiner’s popularity, many climbers choose to utilize the D-shaped carabiner. Why? This carabiner type can directly carry the load away from the gate, reducing the center’s weight - so a smaller, lighter "D" carabiner can be just as strong as a larger oval. 

D-shaped carabiners are a little bit smaller when compared to oval carabiners. As such, they weigh less. In addition, they boast higher durability and provide a stable balance to your load.

Pros:

• Solid and durable.
• Facilitates stable load balance.
• Strongest shape

Cons:

• The D-shape carabiner is more costly than oval shaped.
• It contains a small gate opening, but larger than oval.

OVAL CARABINERS

Oval carabiners are the original style. Most individuals or climbers use the oval carabiner because it has a wide range of purposes, though not quite as strong as other shapes. Among the reasons for its preference by many people is its unique elliptical shape, which creates more space to clip your equipment or gear.  

Another advantage of the oval carabiner is it allows you to hold your weight at the bottom of the oval, promoting a steady climb. In addition, the oval carabiner enables you to descend safely- its symmetrical oval shape provides a braking system. It differs from other types of carabiners in that its weight capacity is minimal. 

Pros:

• Its oval shape creates more space to hold your gear.
• Its center of gravity provided at the bottom of the oval carabiner maintains a stable balance since your equipment will be intact.

Cons:

• Relatively small gate opening.
• Fragile and smooth oval carabiner.

OFFSET/MODIFIED/ASYMMETRIC "D" CARABINERS

This type of carabiner is also referred to as the asymmetric D-shape. It is almost similar to the primary D-shape carabiner, only that it is smaller at one end (to reduce weight). Unlike the D-shape carabiners, modified D carabiners come with large gate openings that provide an effortless clip-on. But they don't have as much inside room as similarly sized Ds or ovals. Many climbers utilize the modified D carabiner.

Pros:

• Decently large gate opening.
• Easy clip-on.
• Lightweight and durable.
• It comes in varieties, including straight and bent gates, double and triple action locks, screw locks, and twists.

Cons: 

• Fairly expensive.
• Less space and weaker than D-shape carabiners.

PEAR SHAPED (HMS) CARABINERS

Pear-shape carabiners are suited explicitly for belay and rappel. Containing a large gate opening, this type of carabiner ensures your gear is safe and secure. Pear-shaped carabiners are used primarily for belaying and rappelling, but also can be used at anchor points for top roping or multipitch climbing. In addition, they help facilitate a stable balance for your load. You’ll sometimes hear these called HMS carabiners, and some are even marked with HMS on the spine. HMS indicates that the carabiner is designed with a wide, more symmetrical top that works well with a Münter hitch.

Pros:

• Features a big gate opening.
• Help facilitate a stable balance for your load.

Cons:

• Costlier and somewhat heavier than most carabiners.
• Not as strong as D and asymmetric D shapes

6 CARABINER LOCKING MECHANISMS

Pay close attention to the type of locking mechanism you will need. 

SCREW LOCK (MANUAL LOCKING)

A screw lock gate carabiner requires the user to manually screw the sleeve onto the gate to lock.  

Pros:

• You can manually tighten a lock using screw locks.
• Easy to use-one can quickly tighten the gate’s sleeve.
• Screw locks are durable and adapt to the dynamics of the environment.

Cons:

• Excess friction on the sleeve tends to unlock the screw lock.
• There is a possibility of forgetting to lock the screw.
• It needs substantial time to fix when loosening the screw lock against the gate.

DOUBLE-ACTION (AUTO LOCK)

Unlocking an auto-lock gate requires two consecutive and distinctive actions. Specifically, releasing an Auto-lock gate requires a rotating sleeve and then manually pushing the lock inwards. Soon after releasing the lock, the double-action carabiner will automatically lock itself. 

Pros:

• Auto-lock carabiners are fast and easy to open.
• The double-action carabiner minimizes the likelihood of forgetting to lock.

Cons:

• The auto-lock carabiner is a shadow to triple-action auto lock’s security.
• Tedious gate opening process- you have to loosen or unscrew its sleeve.

TRIPLE-ACTION (AUTO LOCK)

Unlocking a triple-action carabiner requires you to follow three consecutive steps. The process requires you to shift the sleeve up and down, manually rotate the sleeve, and then push the lock inwards. Like the double-action carabiner, a triple-action carabiner automatically locks itself upon release.

Pros:

• The automatic lock mechanism automatically shuts itself. 
• Highly safe and secure.

Cons:

• Natural environmental conditions like winter or muddy encounters inhibit proper automatic lock function.
• Inconvenient as it mandates the use of two hands.

STRAIGHT GATE (NON-LOCKING)

Straight gate carabiners are a robust and longstanding option, a characteristic that makes them unique. These non-locking carabiners contain a spring-loaded gate that is opened by a single push. A straight-gate carabiner automatically shuts itself and is often used during simple outdoor activities like racking gear.

Straight-gate carabiners are recommended for quick-draw actions. Some of the straight-gate carabiners are inclusive of critical locks to prevent catching and hooking.

Pros:

• Highly durable.
• Render rope clipping process easier.
• Can feature a Keylock-feature, enhancing snag-free clipping.

Cons:

• Heavier than wire gate.

BENT GATE (NON-LOCKING)

Similar to straight-gate carabiners, bent-gate carabiners do not lock and are not recommended for climbing. Their bent shape enables effortless and quick clips, mostly on ropes. They allow for quick-draws at a rope’s end-point.

It is important to note that some bent-gate carabiners brands provide key locking features to avoid injuries and equipment damage.

Pros:

• Highly durable.
• Render rope clipping process easier.
• Keylock-feature enhancing snag-free clipping.

Cons:

• Heavier than wire gate.

WIRE GATE

These carabiners comprise a stainless-steel wire loop gate, which decreases overall weight and eliminates the need for extra parts found in conventional gates. Since they're lower weight, they are also more manageable and more convenient to operate.

In addition, the design creates a wider gate opening. Moreover, these gates are less prone to freezing during cold weather conditions.

Although wiregates don't appear as strong as conventional styles, most are. Also, due to the lower mass in the gate itself, wiregates are less likely to vibrate open during a fall (this is called gate lash).

Pros:

• Relatively lightweight.
• Reduce the likelihood of a freeze shut.
• Reduces the occurrence of gate lash.

Cons:

• Less durable than bent and straight gate carabiners.

SIZE, WEIGHT, AND STRENGTH

SIZE

Carabiners come in a variety of sizes. Large carabiners are typically easier to handle and easier to clip (they have larger gate openings), and they can hold more gear inside. They are commonly used with belay and rappel devices. Smaller carabiners are lighter and take up less room on your rack, but they can be harder to clip.

Gate open clearance, provided in millimeters, is something you may want to pay attention to when looking at the size of a carabiner. This number refers to the width that the gate can open, plus the depth and shape of the bottom of the carabiner below the gate. Generally the smaller the carabiner, the less clearance it offers.

Too little gate-open clearance may lead to your finger getting stuck between the gate and the carabiner body while clipping; too deep a clearance can also make the carabiner difficult to clip. An ideal amount makes clipping the carabiner easy. 

WEIGHT

In general, the less weight you carry with you as you climb, the better. But lighter carabiners are not always best. Superlight carabiners are often smaller, which can make them harder to use when you’re clipping the rope or a bolt. Also, lightweight carabiners often use narrower rod stock, which can mean lower gate-open strengths and shorter lifespans. Narrow carabiners can also cause more rope wear, since the narrow ends can act like edges, biting into your weighted rope as it slides past.

STRENGTH

Carabiners are rated for strength in three directions: lengthwise (major axis), sideways (minor axis) and while open (major axis open or "gate open"). These ratings are typically marked on the spine of the carabinerAll climbing carabiners pass UIAA and CE standards, which means they are plenty strong enough as long as you use them correctly. Gate-open strength and minor-axis strength are where you see the most variation.

Here’s how you might use strength ratings: If you’ve narrowed your search to a few different carabiners that will work well for your style of climbing, look at the strength ratings as one of the final decision points. If one carabiner provides everything you need and is stronger than the others, then you might as well go with that one. Keep in mind that smaller and lighter carabiners are generally weaker than bigger, heavier ones, but not always.