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The Book of Anatomy

“Know what thy is shoving in thou hole.”

The Bolting Bible

The Book of Anatomy

Welcome to our free course as our way of contributing to the bolting community. It's nice to understand what you are clipping and trusting with your life, even if you never plan on installing or removing bolts. Also, if someone is going to spend their time and money to bolt something, I assume, they probably want to do it as good as possible. Hopefully the Bolting Bible gives you the tools you need to do a great job. Get it?

Our courses are A-Z content in blog format, glued together with an over arching blog we call a text book. A blog format is easy to read, easy to update, and easy to translate. Be sure to begin at the TEXTBOOK and at the end of each episode we'll point you to the next.

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.


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

Spike Bolts

coming out, at least for a new bolt, which means they are super duper tight in that hole!. 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.

Nail drives and Drop ins

“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 the 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 its 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

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 installed in harder rock and the bolt could be compromised if trying to install this in a super hard rock. 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 the work horse in BoltBusters but 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. Any hanger test video has these bolts and they are how we test hangers that go to 60kn. It did break once in shear at 46kn on test 66 and after reusing the same hole enough in concrete it will come out like in this VIDEO (at very high forces) Pulling in tension snapped the head off at 43kn as you can see in test 142 (amazing slow mo at 1:15) but it is hard to do as the hangers typically fail first. 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 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 as it won’t hold up to cyclic loading in soft rock. However, they have been used by several climbers in solid rock without any signs of issues and are often used in highly regulated construction. The TitenHD bolts have also been very impressive in Bolt Buster tests.

Mechanical Bolts with Wedges

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 quite a bit if the clip slips, that the threaded rod sticks out so much it gets in the way of carabiners 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.


Believe it or not, bolting companies are not lining up to sponsor us; mostly because there is no money in such a niche industry. $1 per episode helps a ton and so does grabbing MERCH if something grabs your eye. Lots of designs and options.

Removable Bolts

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 (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.. I like using Bolt Products’ welded hangers on fixe triplex bolts so I can thread my rope directly into the hanger.

If you are real experimental and rich, you can try Climbtech's fancy removable anchor. They are designed similar to cams and it 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 if you highline on them it could kink the flexible wire 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 which I always appreciate when someone falls behind their products.

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… tooless. 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. Some previous versions have the hanger fixed on there and not free spinning, so if it is not installed in the right direction and it turns, it would turn the entire bolt in the hole compromising it. A video on installing them can be found here.

Glue-in Bolts

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, if you install a 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 continue 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 is very important to mix it right as most glue in failures is a result of improper mixing. But if mixed right and the hole is dust free, it can offer some of the strongest anchors available.

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.

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. It’s not like 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!

Girth Matters

Back in the day, skinny 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.

Drill bits are important to get right. Although ½” = 12.7mm, you CANNOT interchange 12mm for a ½” drill bit for the Fixe triplex removables because they have a tight tolerance. Also, the Petzl Coeur Pulse requires a 4 point 12mm drill bit so the hole is perfectly round so diameter is really important sometimes. A wave bolt glue in is TIGHT in a ½” hole, so I doubt you could get one in a 12mm hole but fit great in a 14mm hole and is a preferred method if it is not over hanging and you don’t need the tight tolerance. With most glue ins you have a little wiggle room on sizing since it’s the glue holding the rock and not some tiny wings spreading out at the bottom of the hole. You just don’t want to put a ⅜” glue in bolt in a ⅝” hole. Too much of anything is bad. Know your bolt and do a practice install!

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 common 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!


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, see this hanger peel off the bolt in this VIDEO at 0:54 seconds! Use the right size hanger with the right size bolt, but also use washers when applicable. 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.


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

The holes on hangers generally come in 10mm, ⅜”, 12mm, or ½”, 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 even peel off. CMI makes a rare hanger with a ⅝” (16mm) but it is for arborists and not climbing or slacklining. It’s also insanely large which is good if a tree is growing around it but not for the visual impact of our climbing areas.

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 and we have occasionally achieved up to 60kn! CMI’s ⅝ hanger is rated as one of the strongest hangers at a whopping 44kn but broke in our BoltBuster tests as low as 33kn in shear, because it puts too much stress on one side of the hanger. In tension it is full strength. It isn’t made for climbing so don’t buy them. Every hanger made today is as strong or stronger than the aluminum carabiners we will be clipping to them… as long as they don’t corrode.