Climbing anchors without moving parts are collectively known as passive rock protection or "pro." They consist of aluminum pieces in various shapes attached to braided wires, cords or webbing slings.

In contrast, active rock pro features moving parts. The 2 main types are the ubiquitous spring-loaded camming devices (also called SLCDs) and the less common spring-loaded tube chocks.

This article discusses the basics of active rock protection.

Spring-Loaded Camming Devices (SLCDs)

SLCDs (one is shown above) feature 3 or 4 curved pieces of aluminum, called cams. When a spring- loaded trigger wire is pulled, these chunks of metal retract and make the device narrower. This allows a climber to slide the unit inside a crack. When the trigger is released, the cams expand to fit the rock. Placed correctly, SLCDs offer excellent hold, particularly in places where passive chocks and tapers will not.


Most camming devices feature 4 cams. Because of their narrower profile, SLCDs with 3 cams are appropriate for shallower cracks. No matter the number, each cam on an SLCD is individually spring-loaded. This allows the devices to conform to irregular shapes within a crack, with each cam maintaining contact with the rock.

Active camming devices have large expansion ranges. A climber can get a single cam to fit where several different sizes of tapers or hexes might be tried before the correct size is found.

Black Diamond is the only brand of camming device (as of this writing) with double axles or pivot points for the cams. Though they add weight and expense, the twin axles give these cams a much larger expansion range than single-axle varieties.

Rigid Stems

Some SLCDs feature solid aluminum center stems. Although more durable than flexible-wire stems, rigid stems can be problematic in some placements. Take horizontal cracks, for instance. Fall forces could break a rigid-stemmed camming device unless it is placed at an adequate depth or tied off properly. It takes practice to place rigid stems correctly in these situations.

Flexible, Single-Cable Stems

Flexible stems are often the better choice for horizontal placements, but they are not as durable as rigid stems. Single cable stems are narrow enough to fit in narrow cracks or oddly-shaped pockets where other wider stems won't work.

Flexible U-stems

Like single flexible, single-cable stem varieties, U-stems are good for horizontal placements. The trigger on flexible U-shape stems can be operated with the forefinger and thumb, and some climbers find them easier to retract evenly. Some find it difficult to get their thumbs in the curved portion of the smaller size cams.

With any camming device, it's best to get them in your hands and decide for yourself which trigger action is the most comfortable. Comfort and ease of use can make a difference when you're trying to place them quickly with one hand.

Spring-Loaded Tube Chocks

These less common devices consist of spring-loaded, telescoping aluminum tubes. Squeezed together, they contract for placement inside a crack or pocket. When released they expand and hold. Expandable tube chocks are typically used in cracks or pockets more than 6 inches wide. They are commonly used in the uniform cracks found in the Southwest.

Building Your Rack

All styles of cams have their advantages and disadvantages:

  • Those with extra-large size ranges tend to be heavier.
  • Those with rigid stems are very durable but are not as good for horizontal placements.
  • Those with flexible stems are easy to place in horizontal cracks but will wear out quickly if repeatedly fallen on in this type of placement.

Serious climbers who frequent different geological areas often buy different sets of pro to match. But this is impractical (and expensive) if you're just starting to climb and build your rack. One popular concept is to select a full set (typically 7 to 10 pieces) of one brand of SLCDs, allowing you to become familiar with each size. Color-coded, sewn slings help reinforce what size to reach for when faced with a certain size crack.

The most versatile racks have both passive and active protection to handle a variety of routes and types of rock. Be aware that cams can jiggle or "walk" into backward flaring cracks so deeply that they cannot be retrieved. They can also walk out of tapering cracks that widen as they go up. It's good to have passive pro on your rack for upward flaring cracks since it is less likely to be worked free by the rope's movement.

Many new climbers start out with a full set of passive tapers and hexes and add SLCDs gradually. This not only forces them to learn to place passive pro carefully, but it allows those on a budget to climb and still pay their rent.

Practice and experimentation will help you decide on the best type of protection for the formations in your favorite climbing areas.