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The Book of Mechanical Bolts

“Know what thy is shoving in thou hole.”

The Bolting Bible

The Book of Mechanical Bolts

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.


How They Work

Mechancial bolts are simple machines. A wedge gets sucked into something that expands. If it is small clip expanding at the bottom it's a wedge bolt and if it is sleeve over the entire bolt with 2 flanges expanding at the bottom, then it is a sleeve bolt.

Girth Matters

Back in the day, skinny 6mm or 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 bit diameters are important to get right. Although ½” = 12.7mm, you CANNOT interchange 12mm for a ½” drill bit, especially 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. Know your bolt and make sure your drill bit matches.

Length Matters

Mechanical bolt lengths describe the entire bolt so keep in mind how much will be below and above the surface. You can easily lose a 1/2" or 13mm with the hanger + washer + tightening of a wedge bolt. It doesn’t matter how long you think it is but how deep it actually penetrates!

Your length depends on how hard your rock is. 2.25” or 55mm is fine for hard rock. The softer the rock, the deeper you will want the bolt. 6” or 150mm is common for softer rock but if it is really soft or layered rock then you will want a (long) glue in bolt.

Wedge vs Sleeve

Wedge Bolt

Wedge bolts are generally simpler with fewer parts than a sleeve bolt and therefore cheaper. The Powers 5 Piece is a sleeve bolts that has 7 pieces and is finicky to install and is getting quite expensive,

Wedge and sleeve bolts are around the same strength. They are all super good enough. Sleeve bolts however will engage better with softer rock. If you have solid hard rock, wedge bolts are totally good enough.

Wedge bolts pull the entire rod up while the clip stays at the bottom to expand. Because of this, it sticks up when you are done. It's not a problem unless it is in the way of clipping carabiners to it. Sleeve bolts look nice having their heads flush to the hanger since it is just a threaded rod at the end sucking up a wedge-shaped cone. If someone is going to do a bad installation job, a wedge bolt sticking way out is an obvious red flag there isn't much bolt left in the rock but a sleeve bolt keeps all its secrets hidden.

Wedge Bolts in Detail

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.

The real difference is the size of the expansion clip at the base of the rod. There is no real reason to use wedge bolts over sleeve bolts other than it’s easier to find 316SS, as most sleeve bolts are 304SS. So if you have an area that is prone to corrosion and have hard rock (as it’s not a good idea to install wedge bolts in soft rock), then these might be the right choice. But if the area is high risk of corrosion, you might as well put in titanium glue in bolts to make sure that it lasts.

Sleeve Bolts in Detail

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.

Sleeve bolts are better for softer rock because they have a larger surface area and can open the split sleeve wider than just a wedge bolt with a small clip at the end of it. The softer the rock, the deeper and bigger you will want your bolt. There is no downside to using a sleeve bolt in hard rock so it is a good idea to use them unless you want marine grade 316 stainless, which is hard to come by in a sleeve bolt.


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. You might want to remove them because it is a high traffic area. It could be a project that rarely will be repeated. Maybe you are unsure where you want the final bolts during development. 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 use the removables. These also could be a great option for maintenance like in wet canyons where bolts can get damaged by seasonal flooding.