The Book of ANATOMY

"Know what thou is shoving in thy hole"

HowNOTtoHighline Bolting Bible Book of Anatomy Parts of a Bolt for Climbing and Highline Anchors
The Book of Anatomy Bolt Diagram

Some bolts have 5 separate parts and others are just a single rod bent and twisted into shape. Some are welded and some have hangers built into them. Surprisingly, for being just a metal “stick” you shove into a hole, there are a lot of details that go into them as they are basically tiny machines. Know how your little machine works so you know that it will be installed correctly.

Chapter 1 - Types of Bolts

Compression Bolts

Old school button heads have no moving parts. They are cut and shaped to be a little bigger than the hole and have such a tight fit that they stay in. The bolts are called split shaft, the concept is called compression bolts. The little tiny ¼” button heads are found more in blank sections of big walls where bolt ladders needed to be installed, rather than for anchors. The next size up is ⅜” and has a threaded top with a nut. We found while installing them that it takes so much work to pound them in that the nut and hanger have to be preinstalled or the threads get too damaged to put on the nut. We tested these in shear and tension on BoltBuster and found the top of the bolt snaps off before coming out, at least for a new bolt. They rarely come in stainless and is the kind of bolt that is being replaced today. They existed, so we share them here, but please don’t use these. Spike bolts are similar in the fact they are bent but they are the same idea.

HowNOTtoHighline Bolting Bible Book of Anatomy Nail Drive Strike Anchor Threaded Expansion Bolt for Climbing and Highlining
Book of Anatomy Nail Drive Bolt 1

Nail drives and Drop ins

HowNOTtoHighline Bolting Bible Book of Anatomy Nail Drive Hammer Set Strike Anchor Bolt
Book of Anatomy Nail Drive Bolt 2

“Nail drives” or “Hammer set” or “Hammer Drive” or “Strike anchor” or whatever the hell you want to call it, it is a bolt that expands the sides as you smash a nail through the center. If that nail is flush, it isn’t coming out. Petzl used to sell one called the “Petzl Long Life”, clever name for a bolt, but apparently it wasn’t popular enough and was expensive. Some are flush with hanger and prevent hanger thieves, others have nuts that hold down the hangers. Since none available today are designed for life support climbing applications, they are not certified and can be a risk.

ASCA broke an off brand (AALL American) ½” in tension at only 10kn, substantially below it’s MBS. ¼” strike anchors are a popular size online (not for climbing but general use) and those can break below 2kn. Drop in anchors are have a similar design but after the “nail” is pounded in with a set tool, spreading out the bottom flange, and a threaded bolt can be installed onto the threads. This video shows how they work. Short story, just don’t use them, there are much better options these days.

Concrete Screws

HowNOTtoHighline Bolting Bible Book of Anatomy Concrete Screw with Hanger for Climbing and Highline Anchors
Book of Anatomy Concrete Screw w/ Hanger

These work similar to normal wood screws. Pre-drill a hole and the threads bite into the sides of hole. The screws have a cutting thread of harder steel at the tip and the rest of the threads just follow along. This does require a quality impact drill with a ⅜” drive (NOT ¼” like so many are) as it takes quite a bit of torque to get them in, but you won’t need a hammer. The hole doesn’t have to be super clean like glue in bolts require, but you should blow out the dust before installing them, or you may not get it all the way in as the dust in the bottom stops it. Adding some water can help lubricate and cool when installing in harder rock and the bolt could be compromised if trying to install this in a super hard rock.

HowNOTtoHighline Bolting Bible Book of Anatomy Box of Concrete Screws for Climbing and Highline Anchors
Book of Anatomy Concrete Screws

These are NOT safe in softer rock. A ⅜” bolt requires a ⅜” hole (overdrill the length by ¼”) and should be used with a hanger that has a ⅜” hole even though it can feel tight getting it on there. Don’t try to hold the hanger while using your drill to put the bolt in the hole. The threads can grab the hanger and spin around so fast that it could break your hand! The Titen HD’s are what we use in BoltBusters and we found using a hanger with a ½” hole that it would peel off the bolt sometimes in our tension tests, albeit, above 30kn. We use these a lot in BoltBusters to anchor down our hydraulic testers and to test all sorts of hangers as they are easy to remove. We even reused the same holes (in concrete) during our hanger tests over a dozen times and it was still stronger than our hangers even though the hole was being clearly compromised. Some are concerned that after many freeze/thaw cycles these bolts will become loose over time but there hasn’t been enough examples of this problem for us to be concerned about it. These are the easiest bolt to remove and replace from a bolt stewards perspective. They come in zinc plated steel, 304 SS, and 316SS. Please use a stainless that is right for your area.

Keep in mind this is a newer fad and the UIAA or ASCA or any old school bolter does not currently approve of these for the good reason that extensive science has not been done specifically for climbing. Local areas may frown upon this more than others for cultural reasons and these are NOT good in sandstone. However they have been used by several people enough and in construction and in our Bolt Busters tests to include them as a potential viable option for climbing and highlining bolts.

Mechanical Bolts with Wedges

HowNOTtoHighline Bolting Bible Book of Anatomy Mechanical Expansion Wedge Bolt for Climbing and Highline Anchors
Mechanical Wedge Bolt Short
HowNOTtoHighline Bolting Bible Book of Anatomy Mechanical Expansion Wedge Bolt Wear Pattern for Climbing Anchors
Mechanical Wedge Bolt Wearing

These bolts have a small expansion clip with bumps on the side located near the base of a bolt shaft. Those bumps don’t allow it to move since it is slightly bigger than the hole diameter. The very end of the bolt is cone shaped, so when the nut is tightened, it pulls the TAPERED END of the shaft up, expanding the clip. This kind of bolt is recommended only in hard to medium rock as the contact point is very minimal.

Sometimes, this bolt gets extracted so much while wrenching it tight, mostly if the clip were to slip, that the threaded rod ends up sticking up so high that it hinders carabiners from clipping the hangers and leaves significantly less bolt in the rock. If the threaded rod is protruding enough, it could also depress the gate of a carabiner open if the quickdraw was rotated upwards, possibly unclipping it or just reducing strength if loaded in that position. Never use these in sandstone or other soft rock as it can wear down the rock at the contact points under cyclic loads and become loose from the now oversized hole.

Mechanical Bolts with Sleeves

These bolts are threaded rods with a coned nut on the end. These are called sleeve anchors because the sleeve part covers the entire bolt shaft. The hex head and the shaft are one piece, rather than threads at the top with a nut. The “nut” is instead at the bottom and is coned shape so the tighter it is, the more it expands the sleeve. Therefore the hex head stays flush on the hanger rather than the rod sticking out. The sleeve also allows for more contact area and is ok to use for all types of rock although the softer the rock is, the more glue in bolts are preferred. These bolts especially need to be tightened at a specific torque, so if you don’t take a torque wrench with you, practice at home to get the right feel for it before doing your project. If these become loose after placement, they could be prone to unscrewing themselves as the hanger is torqued back and forth by rope tension, and pulling out under body weight. See the buying guide for all your options at the end of the “Mechanical Bolts” section.

HowNOTtoHighline Bolting Bible Book of Anatomy Mechanical Bolts with Sleeves for Climbing and Highline Anchors
Mechanical Sleeve Bolts

Removable Bolts

HowNOTtoHighline Bolting Bible Book of Anatomy Removeable Expansion Sleeve Non Permanent Bolt for Climbing Highline Anchor

Removable bolts are great where you don’t want to leave permanent bolts because it is a high traffic area, a highline that rarely will be rigged, or an overhanging sport route that you need temporary anchors to install better permanent ones. It’s also great if you don’t want to wait for glue in bolts to cure, because these allow you to install the glue ins AFTER you highline on the removables. The concepts are the same as wedge and sleeve bolts, however the harder you pull on those bolts, the more they grab the rock. Contrarily, removables are designed so the sleeves can be pulled up separately after untightening, allowing you to avoid the wedging action that keeps the bolt in the rock. These should not be used as a long term anchor because if they ever were to loosen, they will not be safe to use. Just like all bolts, there are some downsides. They need to be drilled perfectly because if it is too big, it just spins in the hole and if it is too small then it’s a real bitch trying to remove them. If a hole is repeatedly used for a removable, mostly in softer rock, it can wear out the hole, and no one likes a hole that is worn out! If someone tries to repeat a highline, they may not know if it was a 12mm or ½” hole and that’s important because they require different bolts. If on top of a cliff, a hole can get filled in with debris and need extensive cleaning. Also, in my experience, removables can look pretty mangled after a few “removings” so that’s why they aren’t called “reusable bolts” but “removable bolts”. They can be reused but not indefinitely.

Fixe’s Triplex (12mm) has a threaded rod with a tapered cone and Climbtech Legacy Bolt bolt (½”) is a flush hex bolt with a coned nut on the end but is unfortunately no longer available as I have found Climbtech to be easier to remove than the Triplex. Climbtech. I like using Bolt Products’ welded hangers on fixe triplex bolts so I can thread my rope directly into the hanger. See Chapter 5 below for more details on “Hangers”.

HowNOTtoHighline Bolting Bible Book of Anatomy Climbtech Removable Anchor
Climbtech Removable Anchor

If you are real experimental and rich, you can try Climbtech's fancy removable anchor. They are designed similar to how cams are and is just a round version of ball nutz. If you bottom them out (put them in too deep), they will be almost impossible to remove.

These can be great if you need a temporary bolt for establishing a route but I personally wouldn’t highline on them because the flexible wire would probably be kinked after a highline session and the ½” ones are only rated for 11kn. If you use 8 of these for a highline, it should only cost over $600!!! They have ¾” and 1” sizes but we don’t need to be drilling holes in our rocks that big for temporary anchors. You can drill the hole at an angle to minimize the wire kink but if you plan on using that hole for glue, then they need to be drilled properly. The inventor of these does human testing on them in this video.

HowNOTtoHighline Bolting Bible Book of Anatomy Petzl Coeur-Pulse Removable Bolt for Climbing and Highline Anchors
Petzl Removable Bolt

Petzl now has the Coeur-Pulse a 12mm removable that doesn’t require tools (assuming you already have a clean hole waiting for you). Those also are expensive but they can be used for highlining and are pretty fancy. They have a thin sleeve layer that gets pulled out of the way when you pull the trigger… aka… tool-less. They require a perfect hole and so you need to use fresh 4 point bits. The fat heads on them limit how much you can clip to them but I do recommend them if you can afford them. A video on installing them can be found here.

Glue-in Bolts

HowNOTtoHighline Bolting Bible Book of Anatomy Petzl Glue In Bolt for Climbing and Highline Anchors

And now for my favorite... glue-ins! A bolt that doesn’t need a hanger that people can steal, lasts longer than just your interest in climbing/highlining, and they can have static rope directly threaded through them, eliminating 6 or 8 heavy quicklinks or steel carabiners for the lazy highliners. However,

HowNOTtoHighline Bolting Bible Book of Anatomy Threaded Glue in Bolt for Climbing and Highline Anchors

if you install threaded rod (stainless steel please), then you will need a hanger. But if you will be using an anchor for more than one highline and therefore will be pulled in more than one direction the glued in threaded rod can be a good solution. This allows the nut to be loosened and the hanger turned. However, if hangers are removed and replaced often, the threads can get damaged making that bolt worthless. Glue-ins can come as a single shaft with a welded eye on top or a continuous rod. U-shape (or staples) are a rarely used glue in, requiring 2 holes (one for each leg) which is more impact on an area and rare to see as they are prone to unclipping carabiners. Glue always comes in two parts and it is very important to mix it right as most glue in failures are a result of improper mixing. But if mixed right and the hole is dust free, it can offer some of the strongest anchors available.

HowNOTtoHighline Bolting Bible Book of Anatomy Installed Glue in Bolt for Climbing Highlining
Glue in Bolt Installed

Mechanical bolts are just pushing on a fraction of the sides of a hole but glue-ins grab 100% of the hole and that is especially important in softer rock or layered rock. The glue gets into the pores of the rock and makes for a bomber anchor compared to a wedge. It also keeps water out of the hole preventing corrosion where you can’t see it. They are much more technical to install and can cost more (if using hilti epoxy) than a mechanical bolt, but they will last a lifetime therefore leaving less of a long term impact.

HowNOTtoHighline Bolting Bible Book of Anatomy Titan Climbing Titanium Glue in Bolt for Climbing and Highline Anchors
Titan Climbing Titanium Glue In Bolt

Do not use glue with mechanical bolts. You don’t get the best of both worlds, you get the worst. The glue will only sit on the outer sleeve and not attach to the actual rod that holds the hanger down. The glue could prevent the anchors from expanding. If the hole is big enough for glue, the wedge won’t wedge. If the hole is the right size for the hole, there is no room for the glue. The glue can also clog the threads. I’m not saying that a mechanical bolt is going to fall out of the hole easily if you use glue, but that is not how they are designed. Don’t try to get fancy!

Chapter 2 - Girth Matters

Back in the day, ¼ bolts were used and yikes. Now they are all getting replaced. It is very common to have a 10mm or ⅜” bolt for climbing and 12mm or ½” bolts are the standard for highlining since they can potentially see a lot more force than the ones used for climbing. If bolting in softer rock a 16mm or ⅝” bolt might be better, not to benefit from the strength of the bolt, but because a bigger bolt can hold the rock better. And if the rock is soft enough, you will want those fat bolts to be glued in.

HowNOTtoHighline Bolting Bible Book of Anatomy Millimeter Fractional Inch Comparison Chart for Anchor Bolt and Hole Sizes
Millimeter Inch Comparison

Drill bits are important to get right. Although ½” = 12.7mm, you CANNOT interchange 12mm and ½” drill bits if you use fixe triplex removables. Sometimes 12mm and half inch bits can be interchanged for wedge or sleeve. And 12mm or ½” bits are fine for glue ins that require either one. You just don’t want to put a ⅜” glue in bolt in a ⅝” hole. Too much of anything is bad.

Chapter 3 - Length Matters

Your length depends on how hard you are… I mean, how hard the rock is. The harder the rock, the harder the hole, so don’t worry about deep penetration. 2.5” or 55mm is fine for hard rock. The softer the rock the softer the hole and so you want to get it in as deep as you can. 6” or 150mm is important for softer rock.

Remember, mechanical bolt lengths describe the entire bolt so keep in mind how much will be below and above the surface. Glue ins are often measured by just the section that goes inside the rock. It doesn’t matter how long you think it is but how deep it actually penetrates!

Chapter 4 - Washers

Washers distribute the pressure over more of the hanger (serious rocket science material here!). They might not be fancy but they are important. Some bolts, like Powers 5 piece rawl, comes with the washer. They are also very important if chain links are used instead of hangers (which is not an ideal method). In BoltBusters, we tested with and without washers on ½” holes on ⅜” holes. The hangers would peel off the bolt! Use the right size hanger with the right size bolt, but also use washers when applicable.

HowNOTtoHighline Bolting Bible Book of Anatomy Rusting Zinc Washer on Bolt and Hanger Climbing Highline Anchor
Rusted Washer on Bolt Hanger

The most common mistake when using washers is to buy the shiny cheap ones at the store. Don’t use zinc washers! Stainless and stainless need to be together or that washer will rust quickly.

Chapter 5 - Hangers

HowNOTtoHighline Bolting Bible Book of Anatomy Stainless Steel Bolt Hanger for Climbing Highlining Anchors
Climbing Bolt Hanger

We aren't talking about the airplane kind or the closet kind, but climbing hangers… and they are not all created equal.

The bolt holes generally come in ⅜”, 10mm, ½”, 12mm and CMI makes a rare hanger with a ⅝” (16mm) and if you ask nicely, Jim Titt from Bolt-Products sometimes makes his awesome welded hangers in the bigger size. It’s important to use the right size bolt with right size hanger, otherwise it floats around the bolt and can twerk it wrong. And we shouldn’t be twerking around our holes! We have also had many ½” hangers peel off our ⅜” bolts (under quite a bit of force).

HowNOTtoHighline Bolting Bible Book of Anatomy Various Types of Bolt Hangers for Climbing and Highlining
Bolt Hanger Examples

The hanger strengths vary on normal size hangers around 25kn but Fixe's stainless ½” and 12mm hangers are 30kn certified with a 44kn ultimate breaking strength. We have occasionally achieved up to 60kn on Fixe’s PLX and SS hangers in our BoltBuster tests. CMI’s ⅝ hanger is rated as one of the strongest hangers at a whopping 44kn but broke in BoltBuster at 37kn, 15% below the MBS because they use a cheap mild steel that they powder coat instead of using Stainless steel which would be stronger and last longer.

HowNOTtoHighline Bolting Bible Book of Anatomy Hanger Materials Matter Corrosion on Climbing and Highline Anchors

The materials that hangers are made of also vary. I don’t know why aluminum hangers exist, but they do. They are not as strong and it mixes metals. Fixe sells PS (plated steel) and saves very little money in exchange for strength (about 10kn less) and longevity (don’t use zinc plated anything!). These are probably intended for indoor use such as climbing gyms. As amazing as the large CMI’s hangers are, they are just powder coated plated steel so that really kills the stoke I had for them, even before they broke a lot lower than their claimed 10,000lbf. Stainless steel hangers are the only kind of materials that should be used for hangers since we should only be using stainless steel bolts (or titanium but those don’t come in a mechanical bolt so you don’t need a titanium hanger). Fixe and Petzl both sell 304 stainless hangers. Fixe also sells a 316 stainless hanger and a PLX hanger which we have found to be the strongest on the market in BoltBuster.

HowNOTtoHighline Bolting Bible Book of Anatomy Bolt Products 12mm Stainless Steel Hanger for Climbing and Highline

Bolt-Products makes a 12mm (the size of the bolt hole) hanger out of 8mm stainless rod so rope can be threaded through. Not ideal for climbing anchors as it would wear the metal quickly but eliminating the need for quicklinks in highline anchors since ropes cannot be threaded directly into normal sharper hangers. The downside is that it is welded, increasing the risk of SCC (stress crack corrosion) in certain harsh environments, and the weld point is a risk point of failure (though unlikely). They are rated for 45kn and we could NOT break them in tension at 42kn and in shear at 52kn (bolt heads snapped off first) so we are very happy with strength. They are a great solution to be able to run the rope directly in the hanger, which you cannot do with a normal hanger. In fact, the only solution for direct ropes if using mechanical bolts other than chain links.

HowNOTtoHighline Bolting Bible Book of Anatomy Bolt with Rope Through Chain Links Climbing Highline Anchor
Bolt with Chain Links

Chainlinks are commonly used as a cheap “hanger” that a rope can be threaded in for highline anchors and is generally rated for 30kn to 70kn. Basic new steel chains used on ⅝” bolts that we tested in sandstone broke in the 60kn range when they broke. The bolt broke more often. One downside is that they rust because no one buys high quality chain links. The other problem is they don’t sit flush with the rock, meaning they pull on the bolt about a half inch above the rock, creating a lever that greatly reduces the strength of the bolt. Also, if you see chains, there is a 90% chance there is a zinc plated bolt in the rock since price was the obvious deciding factor when installing the anchor. One chain link cannot be used, but instead 2 or 4 links need to be used to get a proper orientation and consider the more links, the more points of failure there are. These chain link bolts should only be used to pull shear (sideways) and should not be used to pull a bolt in tension (straight out) because it deforms the chains significantly even though we got around 50kn before final destruction of the chain happened. We do not know the strength of zinc plated chains after corrosion has begun.


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