How Climbing Bolts Work: Know Your Pro
If you’re into sport climbing, you probably don’t think twice about clipping bolts, happily moving past them with mental ease. If you’re a trad climber, a climbing bolt may offer peace of mind for a safe rappel — or it could be a relic of questionable safety.
Editor’s note: This article is not intended to be used to determine the safety of bolts, but rather for educational purposes and background information only!
So, how do you know what to look for and judge what is safe? Or better yet, how do climbing bolts even work in the first place?
Climbing Bolts: How Do They Work?
Types of Bolts
Climbing bolts come in a few forms, with the most common being a simple mechanical expansion bolt. Mechanical expansion bolts can be either a “wedge bolt” or a five-piece “sleeve bolt.” We will dig into the differences shortly.
Other commonly accepted bolts found on climbing routes, especially in softer stone or corrosive environments, are glue-in bolts.
On very old routes without updated modern hardware, a number of styles of unsafe bolts may be found. However, we will focus only on modern bolts in this article.
In addition to the bolt that actually anchors into the rock, a hanger is placed, which is the hardware the quickdraw engages. Hangers mostly look the same, but again, there are some very old models of hangers that are questionable.
In its simplest form, mechanical bolts all work the same. a hole is drilled in the rock with a hammer drill and masonry bit, and the hole is cleaned with a brush and blowing tool. Then the bolt is hammered into the hole with the hanger attached, and the bolt is tightened to secure it into the rock.
Wedge Bolts
In the case of mechanical “wedge bolts,” the tightening process of the bolt pulls a cone of metal at the end of the bolt into a small split cylinder of metal that expands and compresses into the surrounding rock. This compression is the primary holding force of the bolt.
Wedge bolts are commonly used in very hard, durable rock types such as granite, gneiss, and hard quartzite.
An example of a commonly used wedge bolt in climbing is the Powers 304 Stainless Steel Wedge Bolt.
Sleeve Bolt
Similarly, in a five-piece “sleeve bolt,” the same wedge is pulled up the threads upon tightening, but instead of a small section, the entire outside “sleeve” of the bolt is split. More surface area of the sleeve and, therefore, the bolt comes into contact with the rock compared to a wedge bolt. This delivers more holding power.
For that reason, sleeve bolts are often used in softer rock types such as sandstone, where having more of the sleeve of the bolt in contact with the rock spreads the forces out better inside of the bolt hole.
Both wedge and sleeve bolts typically come in diameters of 3/8 inch to ½ inch in diameter and anywhere from 2¼ inches to 4¾ inches in length. Route developers choose bolt dimensions depending on rock type and quality. Plated steel and stainless steel versions are sold, with the stainless steel costing more but they are more durable in humid or wet climates.
A common five-piece sleeve bolt used in climbing is the Powers Stainless Steel 5-piece Bolt. Some climbing-specific brands also sell bolts, like Petzl with their Stainless Steel Coeur Bolt and Hanger.
Glue-In Bolts
Lastly, glue-in bolts are typically reserved for very soft or porous rock types such as limestone or very soft sandstone. Route developers also prefer them for areas subject to corrosion, like sea cliffs. In these cases, noncorrosive materials like titanium are common.
Glue-in bolts are considered to be very strong and longer-lasting than mechanical bolts but take longer to install and require more specialized knowledge.
For glue-in bolts, after the hold is drilled and cleaned, a glue gun is used to fill the hole with specialized high-strength glue, and the bolt is placed into the glue in such a way that it comes into contact with the rock and the glue without any air bubbles forming inside.
The strength of the bolt relies upon the high-strength glue bonding the bolt to the entire surface area of the bolt hole. In this way, glue-in bolts typically achieve higher strength ratings due to the large surface area of the bolt and the glue bonded to the rock.
Glue-in bolts do not need a separate hanger, instead having a smooth eyelet built-in. Not only does this eliminate the potential of loosening over time, but the smooth eyelet also allows running the rope directly through the bolt. This potentially eliminates hardware at the belay station or the top of a single-pitch route. It also allows “bailing” mid-route without leaving anything behind or other shenanigans.
Popular glue-in bolts are the ClimbTech Wave Bolt and the Petzl Collnox.
Materials
Climbing bolts are made of many different types of metal. The important metric for climbing-grade quality hardware is stainless steel (at a minimum), with all components like hangers being the same grade of stainless steel. If different metals or metal grades are used, galvanic corrosion can occur between components and degrade the hardware.
Common climbing hardware is often 304 or 316 stainless steel. Importantly, zinc-plated or plated stainless steel hardware is not suitable for climbing, as the plating breaks off and chips over time, allowing corrosion to the steel underneath.
In corrosive environments near the beach, often titanium glue-in bolts are used as they do not corrode.
Popular hangers are the Metolius Stainless Steel Bolt Hanger, the Fixehardware 316 SS Bolt Hanger, and the Petzl Coeur Stainless.
Conclusion
At the end of the day, all climbing bolts are not equal, and it’s worth knowing which types of old bolts demand suspicion. We rely on these simple mechanical devices to anchor us safely to the wall, so we might as well know how they work!
Take a look at the Access Fund’s article on safe climbing bolts and hardware.
Climbing Explainer: Belaying for Top Roping vs. Leading
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