Bolt Basics: What Every Climber Should Know

by Jason Haas

The state of bolts in America
How to determine if you can trust a bolt
Identifying bad hangers

The state of bolts in America

In the early days of bolting, climbers were venturing into the unknown, using a wide variety of construction bolts. Route developers of the day lacked a clear understanding of how different bolts performed under the loads generated by a fall, or of which types of bolts might work best in which types of rock, or even of which types of bolts might be more susceptible to the mysterious and complex forces of corrosion in which types of climates.

Without standards or reliable data, decisions on what bolting hardware to use were often driven by ease of use and accessibility, personal preference, and cost. Still, if placed correctly, most bolts used in climbing were reasonably safe on the day they were placed. However, the metal in every bolt chemically reacts with its environment over time—though the reaction can be faster or slower depending on the climate and rock type—and the metal composition of many bolts has proven to be ill suited for its application.

Stainless steel bolts, the standard we recommend in most cases today, are fairly resistant to corrosive forces. But the bolts of yore were not stainless steel, which means they were plated steel. In layman’s terms, plated steel is more affected by the elements and more susceptible to corrosion—much more.

Even plated steel bolts placed as little as five years ago in the Owens River Gorge and at Joshua Tree, two of the driest climbing areas in the United States where you might assume rust wouldn’t be an issue, have significant rust problems under the surface.

In other words, age alone cannot be used to determine whether a bolt is in good condition. The importance of age really has to do with how long the elements have been impacting the metal. While most climbers think of this impact as water and thus rust, corrosion can be caused by other elements in the environment. Salt, for example, which contains chloride, can cause stress corrosion cracking. Many climbers know that salt has had had a huge impact on seaside cliffs near the ocean, but salts can also be an issue with inland karst formations, such as limestone and dolomite.

Climbers in the ‘80s, concerned about water speeding up the corrosion process, began sealing the bolt opening with glue. This not only prevented people from chopping their routes during the great bolt wars of the time, but it also kept water out—or so they thought. In fact, it sometimes did the opposite by trapping moisture in the hole as rock is porous and water can still work its way to the bolt. In those cases, the water just had a harder time leaving, creating unsafe bolts sooner than may have otherwise happened.

Even bolts placed in the ‘80s in relatively dry climates without concern for water or salts are likely much less safe today. Colorado State University professor Paul Heyliger has been testing the shear strength of old bolts and found that bolts placed in the ‘80s in the granite of Colorado’s South Platte, a place with minimal moisture and far from any other corrosive concerns, such as ocean salt, have been weakened by more than half. Their sheer strength—the amount of force it takes to snap off the bolt right inside the hole—now averages only 4,000 pounds compared to about 8,000 pounds when new. That’s quite a big difference when you realize that a 175-pound climber can generate 3,200 pounds of force or more during a lead fall.

The combination of non-stainless steel bolts, climate, rock type and well-meaning but sometimes counterproductive installation techniques means that, today, the quality and safety of fixed hardware ranges from very good to abysmal.

What kind of steel is that bolt made of?

In the past, route developers have not often used stainless steel bolts, which are more expensive. But their superior ability to resist corrosion means that stainless steel should be the standard for climbers today. Even so, many developers who are placing bolts now may not know what kind of steel the bolts in their tool bags are made of.

Here’s two quick ways to find out: First, if your bolts don’t specifically say stainless steel, they’re not. Second, you can use the magnet test. If a bolt gets instantly drawn to a magnet, even a refrigerator magnet, it’s made of plated steel. Stainless steel has some conductivity but not a lot, meaning your magnet will most likely move the bolt, but you shouldn’t be able to pick it up off the ground with just the magnet. The same goes for hangers – although most (but not all) climbing hangers sold today are stainless steel.

What’s rock type got to do with it?

Not all rocks are created equal. Rock strength can vary significantly by rock type and can even vary within the same rock types. “Good” granite, for example, varies in compressive strength—the maximum force that can be applied to the rock before it breaks—from 4,000 to 40,000 pounds. Sandstone is highly variable, ranging from the soft desert sandstone of Utah to the bullet-hard rock of the New River Gorge. In terms of compression strength, “good” sandstone typically ranges from 1,000 to 20,000 pounds. Limestone is weaker than many climbers realize, though it varies much less than granite and sandstone, typically checking in somewhere between 1,000 and 5,000 pounds.

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How to determine if you can trust a bolt

All bolts become weaker with age and exposure to the elements, but there are two types of bolts that are the most typical “junk” you’ll find in the rock—though there is a virtually endless amount of hardware store mank that can be found on routes.

Climbers should be wary of all button heads, a type of compression bolt that is typically only 0.25 inches thick and 1.25 inches long. Button heads have a split shaft, which means less than half of the 1.25 inches of length is actually pressing against the bolt hole to keep it in the rock. There are numerous incidences when these types of bolts have been removed with little more than a few hard jerks using a quickdraw. These bolts can vary in pullout strength in granite, but consider them downright dangerous in softer rock, such as sandstone or limestone.

Another suspect bolt type is Star Dryvins, typically called star drives, can be identified by the star stamped on their heads. Star drives tend to have a greater degree of variability in terms of how bomber they are. Sometimes they come ripping out of the wall with a quickdraw yank, but at other times, they can prove quite difficult to remove.

While button heads and Star Dryvins are red flags by themselves, other bolts may still be dangerous. Even bolts that were specifically designed for rock climbing—rather than construction uses like button heads and star dryvins—rust and corrode with age. Keep an eye out for any visible rust. On a typical wedge bolt, the outer threads and nut may be blackened with rust. For sleeve bolts, you can unscrew the hex head and pull the bolt out to examine the degree of corrosion occurring inside the sleeve.

Sometimes a bolt that would otherwise be totally safe is unsafe because of where the bolt is located. Bolts placed in fractured rock and hollow flakes or too close to the edges of overhangs or arêtes may fail because the rock itself isn’t strong enough to withstand the force of a fall. Bolts have sometimes even been placed in blocks that turned out to be wholly detached from the wall.

Spinners”—loose bolts and hangers—also warrant caution. Most people who have been climbing for a few years have probably experienced a spinning bolt that can be tightened by hand. This accounts for the vast majority of spinning hangers out there, and these bolts do not need to be replaced. They simply need to be tightened to the correct torque recommended by the manufacturer, a specification that can vary widely from bolt type to bolt type.

But a bolt that is loose and wobbly in and of itself is more of a concern. The easiest way to identify this is if the whole bolt still wiggles after the nut has been completely tightened with a wrench or if you can’t tighten the bolt down because it simply spins inside the hole. Those types of “spinners” are unsafe and need to be replaced.

Even bolts that seem bomber in every way may still have been weakened by the stresses caused by repeated falls. When climbers fall, they swing out from the wall and place a bending load on the bolt, which stresses the metal more than the same magnitude load applied in other manners.

Falls also create several loading conditions simultaneously, which are both additive and potentially dangerous. A bolt that is exposed repeatedly to these loads—such as the bolt protecting the crux of a local classic—could become severely fatigued.

This fatigue can cause bolts to fail at a much lower strength than they are rated at. When bolts are strength-tested by the manufacturer, loads are applied slowly and smoothly in increasing magnitude until the bolt being tested fails. This is not how climbers load a bolt; climbing falls are quick and dynamic. Tests have shown that bolts loaded by repeated back-and-forth bending motions will fail at as little as 10 percent of the rated strength.

This type of metal fatigue might be familiar to you—it’s the same phenomenon that helps you remove tabs from beer cans. Again, these bolts may look totally fine, but be aware that crux bolts may need periodic upkeep when the rest of the route is totally fine.

How tight should that bolt be?

Bolts have a specified level of torque the manufacturer recommends. For instance, a 1/2-inch plated steel five-piece Powers sleeve bolt is rated to 40 foot-pounds of torque while the exact same bolt in stainless steel should only be tightened to 25 foot-pounds. When you place a bolt, it is always best to use a torque wrench to tighten to the specified amount. However, bolters do not always use a torque wrench and instead it’s typical for people to tighten to “feel.” While torque wrenches are expensive and heavier than a typical crescent wrench, simply using a crescent wrench can be an unsafe practice, especially for those new to bolting. If a bolt is over-tightened, it can break. Or worse yet, almost break, thus potentially failing when a climber takes a lead fall onto it. If the bolt is under-tightened, it can quickly loosen up and become a spinner.

Tension strength vs. shear strength

Corrosion can weaken a bolt’s tension strength, also called pullout strength, as well as its shear strength. Tension strength refers to how much force it takes to pull a bolt out of the hole in which it was placed. (Imagine clipping a carabiner onto the hanger and trying to jerk the bolt out.) Good tension strength allows the bolt to withstand the force generated from a fall, whether on a slab or an overhang. Shear strength, on the other hand, deals with the bolt snapping off, typically just inside the hole, when a load is applied straight down or when the bolt is over-tightened. A typical stainless steel five-piece Powers sleeve bolt—which has a 1/2-inch diameter and is 2.5-inches long—has a tension strength of 7,320 pounds and a shear strength of 8,225 pounds in 6,000 psi concrete, roughly the equivalent of most granite.

Identifying bad hangers

There are three main factors that contribute to hanger safety: what type of hanger it is, how worn the hanger is, and whether the hanger metal type matches the bolt metal type.

First and foremost is the type of hanger used. One of the most unsafe type of hanger a climber will come across is a Leeper hanger, which are easy to identify by their typically blackened color and semi-sharp edges compared to the rounded shape of a modern hanger. Leeper hangers were the first commercially made hanger designed specifically for climbing. However, because they were the first, not all the kinks had been worked out before they went into mass production, and in fact, they were eventually recalled. But the recall didn’t occur until entire crags were fully equipped using those hangers.

Leeper hangers are more typical in climbing areas that precede the sport climbing revolution of the ‘80s and ‘90s, and you’ll often find them at anchors or on mixed routes that only have a few bolts protecting them rather than fully equipped sport routes. The hangers have been known to fail when they’re pulled on to help remove the bolt, and they’re frequently the culprit when the force of a lead fall breaks a hanger. They are often weaker than the button head or star drive bolt they are attached to.

But before Leeper hangers were homemade hangers, which should also be treated with great suspicion. These homemade pieces ranged from hacked-off bedframes to full-on weld jobs. Some areas, such as the Red River Gorge in Kentucky, originally had loads of these homemade hangers. In the Red, Porter Jarrard was nearly as famous for his hangers as he was for his iconic sport routes. Because these types of hangers are homemade and vary greatly, their ultimate strength cannot truly be known, making their safety questionable. For one, they are not stainless steel and have been in the rock a really long time, so the forces of corrosion have been at work for decades.

Another type of hanger to be concerned with is the thin SMC hanger. SMC hangers in general haven’t been produced since the ‘80s, so any bolt with an SMC hanger on it should probably be on a “to-do” list for bolt replacement.

SMC hangers came in two widths. The thin hangers—which are almost exactly the width of a single quarter—were used from the late ‘70s to early ‘80s and are nearly as bad as Leeper hangers. The newer, thicker hangers placed later in the ‘80s are about the width of two quarters and are stronger.

The two types of SMC hangers can also be distinguished by the way SMC was stamped into the metal. The older hangers were stamped with “SMC” horizontally while the newer hangers were stamped “SMC” vertically. In addition, the thin hangers are plated steel and are highly magnetic while thick hangers are stainless steel and are not as magnetic. Thin SMC hangers also tend to “age” and have a yellow tinge that eventually turns black. If paired with a stainless steel bolt, the thicker, stainless steel SMC hanger may be safe for now. The question then becomes much more complex and nuanced. What type of bolt is it paired with? Is the bolt in overhanging rock? These hangers are much better in a slabby to vertical orientation. Keep in mind again, the bolt/hanger is probably close to 30 years old so while the bolt may be safe today, it should be on the list for replacement at some point.

Cold shuts—which have been used on routes as recently as the ‘90s—should also be added to the list of hardware that will need to be updated. There are two types of cold shuts, open and closed, and both are dangerous. Many cold shuts were welded in a climber’s garage. Explaining the danger of that, Sandor Nagay wrote in Climbing magazine, “None of us would climb on a rope that our buddy wove in his garage, but many of us trust cold shuts implicitly.”

Nagay, a mechanical engineer, and Will Manion, a civil engineer, did extensive testing with cold shuts, including both 3/8-inch and1/2-inch versions. The variances in strength were extreme, ranging from 2,120 pounds to 8,180 pounds, with almost all of them failing at the weld. By comparison, most modern bolt hangers have an average strength of at least 6,400 pounds, about twice the force a 175-pound climber can generate during a lead fall. Nagay and Manion also found that cold shut strength was not consistent even among batches of new, unused cold shuts from the store. It should be noted that study was done in 1997, when most cold shuts were fairly new. Because of the variability, much like homemeade hangers, they should be replaced.

Regardless of type or brand, worn hangers also are a concern. The inner edge of virtually any modern hanger—where the carabiner rests—is relatively sharp and not meant for rappelling off of directly. When this inner edge gets nicks or burrs on it, it can transfer that damage to your carabiner and, ultimately, your rope. Damage to the hanger’s edge can be caused by a variety of things, including whippers, hang-doggging and rock fall. But fortunately, it’s easy to see.

Hangers with smooth edges—such as cold shuts and Metolius Rap (aka Fat) Hangers—also become worn, but the damage is different. The worst offender among the smooth hangers are open cold shuts, which are just what they sounds like: The metal does not form a solid, or “closed,” loop sealed with a welded joint. This allows climbers to simply drape the rope over them and lower down, and they’re used almost exclusively for single-pitch anchors. The problem is two-fold. First, the hanger is simply not that strong and is prone to bending and “opening” even more. Also, because they are designed for looping the rope directly over them, climbers tend to lower and toprope directly through them, causing wear more quickly.

Chains that are attached to anchor bolts with spacer washers are also dangerous. This set up can be as deadly, if not more so, than the infamous American Death Triangle-style of webbing anchors because it causes the bolt to stick further out of the hole, thus bending the bolt. Aside from the fact that the bolt is not in the hole as deep as it should be, the quality of chain that was used is not likely to be very high.

Lastly, hangers that are made of a different type of metal than the bolt they are attached to are a huge safety concern. When metals are mixed, galvanic corrosion starts to happen at an alarming rate. Typically, this happens when the hanger is stainless steel but the bolt is zinc plated. Sometimes, the mixed-metal scenario is introduced when a well-meaning climber replaces only the hangers on the route and not the bolts. This can create the illusion of a safer route with solid-looking bolts, but beneath the surface, the bolts may now be corroding at a quicker pace.

Last photo courtesy of Salt Lake Climbers Alliance

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