The Book of MECHANICAL BOLTS

"The more you twist the head, the more the nut gets sucked up"

Mechanical Bolts Example 1

So mechanical bolts aren’t rocket science. If you have the right size hole, and a quality bolt made of stainless, the basic idea is that you smash it in and tighten it. A wedge gets sucked into something that expands. You can have a rod with a flared end or wedged nut, and if the part that expands is big enough, it’s no longer a plain ol’ wedge bolt but magically transforms into a sleeve bolt. However, like everything, it’s what they don’t tell you that gets ya… so let's go over the little nuances of each type of bolt that will help you install a safe mechanical bolt.


Chapter 1 - Sleeve Bolts

Legacy Bolt Cone Diagram

Smash them in and tighten them. It’s not much harder than that, but here is some stuff you need to know. It is important to install the hanger onto the bolt BEFORE hammering it in. If you forget, then you may not be able to pull it back out to get the hanger on. If you can partially remove it like the Power-Bolt, then you risk debris getting into the threaded cone at the bottom.

If you take the nut off of Fixe’s Triplex bolt, then the whole rod can fall into the hole and probably deep enough to where you can’t get it out because there would be no way to grab it. So, install the hanger of your liking to the bolt BEFORE hammering it into hole. Place the coned nut, that is at the bottom, so it is just touching the sleeve but don’t pre-expand the sleeve (see pic above).


Now it’s time to hammer it in (the hole is clean, right!?). If it goes in really really easy, you may have a hard time getting it to tighten because the entire bolt and all its parts are spinning in the hole. If it is a bitch to get in the hole, then your hole is too small and you risk breaking or compromising your bolt, and the harder it is to get in a removable, the harder it will be to get it out!



Then tighten it. All bolts have a specific torque pressure they require to achieve the ratings that the manufacturer claimed. Torque wrenches are not expensive but can suck to take on a long hike. If you don’t use one on the mountain, at least use it on some practice bolts at home in your backyard so you know what it should feel like. If 25 foot lbs of torque is required and you have no freaking clue what that feels like, use a small to medium wrench and pull until your face scrunches but not so hard that you grunt. If you don’t tighten it enough, obviously the risk is that it could come out. When I tensioned bolts from 25 to 35 torque lbs, I was shocked how much umpf I had to give it. There is a limit, like everything, that if you really really tighten it that you compromise its integrity by breaking the bolt or stress cracking it. A fun experiment is to try to pull out your test bolts after hardly tightening it at all. It is amazing how well they hold. However it is important that they are properly tightened.


Mechanical Expansion Bolt Example




Hangers want to be a certain direction depending which way you pull them. You don’t want to randomly place your hanger and then, when tension is applied to it, forces it to spin to the correct orientation while under pressure. If it doesn’t spin, then you are pulling on that hanger in a very unfavorable way, just as if you pulled against the gate of a carabiner. It can reduce the strength. Hangers broke lower in our tension tests on BoltBusters than in shear. Put a carabiner on the hanger and pull on it in the direction it will be used. And on highline anchors, remember that the furthest outside bolts are going to be pulled diagonally towards the master point, and not necessarily the same direction as the highline.

Keep in mind that if your hole is too shallow, the bolt obviously won’t go in all the way, but that means the hanger will be spinning because it isn’t secured to the rock. That doesn’t mean it will blow out the hole if you use it, but it is considered sloppy and I don’t know if I would trust a bolt that I knew nothing about if the hanger is loosely spinning. If you really goofed, and it is sticking way up, then it could leverage the bolt, breaking it at a much lower force.

Mechanical Wedge Bolt Example 2

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.





Chapter 2 - Wedge Bolts


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.

To install, start in the same way as the sleeve bolts by putting the hanger on the bolt before hammering. These too require a specific torque. Tighter isn’t always better. Be sure to line up your hanger with the direction you will pull it and wrench it down. The rod will stick up higher than the nut after you torque it so start with the nut as high as possible without hitting it with the hammer. Make sure the wedge is expanding immediately and not sliding up the hole walls as you tension the nut 20 turns, leaving very little bolt left in the rock.





Chapter 3 - Are you an Innie or an Outie?


Bolt Installation Example

Ok, so bolts don’t have innies as much as flush hex heads. A hex head attached to the rod sucks up the nut at the bottom like a good cough will do to yours! The rod/shaft doesn’t get any higher the more you tighten it; all the magic happens in the hole. Only sleeve bolts have this design.


But then there are outies where the rod/shaft is being pulled out of the rock as you tighten the nut. This can be on some sleeve bolts, but it is on every wedge bolts. The nut should be installed when you hammer it in, but you don’t want to hit the nut because that means you are putting all the force on the threads and that can damage them. However, you don’t want the rod sticking way up when you are done, so you want to start the nut as high as you can get it, without actually hitting it.






Chapter 4 - Hangers Matter


Bolt Hanger Example

The hanger that the bolt is securing to the rock, is as important as the bolt itself. Many hangers are rated for 22kn to 25kn just like the carabiners climbers generally attach to them. However some hangers have broken past 50KN as seen in our BoltBuster tests. It is nice to have a hanger that is similar strength to the bolt it is attached to, otherwise you could be leaving some strength on the table since the weakest link will break. Hangers made from round stock can have rope threaded directly into them for highline anchors. The round stock generally has less of an impact as they don’t shine quite the same way as a flat hanger, so that can be a benefit to using them in climbing, but is not ideal for climbing anchors as they could wear down quickly if ropes are constantly running inside of them. Offset hangers are designed for anchors so your rings or quick links added to them allow the rope to go sideways and not get smashed against the rock. Additional hardware should be added to hangers for climbing lower off anchors.


  • Fixe Hardware has some SS hangers that have a Ultimate Breaking Strength up to 44kn or 10,000lbs, and are CE/UIAA Certified for 30kn. In BoltBusters, we have confirmed the ultimate breaking strength to be a common result. The PLX hangers are really strong! They come with hole sizes 10mm, ⅜”, 12mm, ½” from $2.95 to $3.95. DON’T BE A CHEAP ASS AND BUY THE PLATED STEEL HANGERS. THOSE ARE FOR INDOOR GYMS.


  • Petzl has a 316SS hanger that is about $4 each but they are only rated by Petzl for 25kn.


  • CMI has a hanger for a ⅝” bolt and is powder coated steel. Since we can’t mix metals and shouldn’t use anything but stainless, these probably shouldn’t be used. We also broke them at 15kn below MBS. And they are $10.35 each! Not recommended.


  • Bolt-Products has a hanger made from a 8mm 316SS (A4) welded rod for a 12mm bolt at a price of €5.20. These allow a rope to be threaded directly inside of them. These are my favorite hanger. They work great with Fixe’s Triplex Bolts or any 12mm bolt that you have. I have to drill the hole slightly bigger if I want to use them on ½” bolts. Team Tough is the US distributor for Bolt-Products.





  • Bonier has a hanger without sharp edges so that a rope can be threaded through, which is ideal as a highliner since we won’t have the rope running over this surface wearing it out like a climbing anchor. Comes in 304 and 316SS



  • Bonier also has an omnidirectional hanger for 12mm or ½” bolts, though power bolts will NOT work with it because this gets set on a bolt after it is installed. Certified for the construction world but possibly a great highline hanger for lines pulling straight out of a wall.



  • Chain links require many washers between the link and the rock to raise it high enough so the second link doesn’t grind on the rock. This means all the pressure is being put towards the top of the bolt instead of the base, significantly reducing strength. Also, they should not be pulled in tension, so if you put your bolts in the middle of a cliff face to be pulled directly outward, chain links should not be used. Keep in mind these don’t work for sleeve bolts (because of the flush heads) so then wedge bolts are most likely going to be used which isn’t the best option but OK if stainless. The one good thing about them is that they can have a rope threaded in them eliminating the need for quicklinks in a highline rig. However, chain links you may see at highlines are probably zinc plated because cost was the determining factor when installing them. 1st Chain Supply also offers ½” made from 316SS but it is 14.90 per foot with a 10 foot minimum.

Bolt with Chain Links and Rope



Chapter 5 - Uhg, why is it doing that? (FAQs)


  • Why is my sleeve bolt just spinning and not getting tighter?

The hole is probably too big, the entire bolt and all its parts are spinning inside. The nut at the bottom of a sleeve bolt needs to stop spinning, so give friction to the nut by pulling up against the sleeve while you tighten. This is done by pulling up/over on the hanger. If it comes out too much, after you get some progress, hit it back down flush against the hanger and rock and finish tightening it.


  • Why is the wedge bolt rising as I tighten but not getting tighter?

The clip at the bottom is either spinning with it or the wedge at the bottom is lifting the clip instead of expanding it. The clips commonly have 2 bumps on them to give some friction along the rock and so it shouldn’t do this, but if that’s your problem then try to pull up on hanger while tightening but if you try to hammer a wedge bolt back down because it got to high/extracted, it only knocks the wedge out of the clip and you are more or less starting all over. Hole size is pretty important here.


  • Why is it snug and tightening but won’t get solid?

If you are sure the sleeve or clip is expanding and it is snug but not increasingly getting tighter, then the rock is shit and it’s expanding the rock (I have had this happen to me before in Iceland).

  • What are those plastic parts on the sleeve bolts?

Plastic Parts on Mechanical Bolts

Sometimes there are spacer sleeves or bushings or compression rings that are made out of plastic. These just separate the parts and it’s not holding any force but helps with installation. The powers spec sheet states, “The Power-Bolt is also designed to draw the fixture into full bearing against the base material through the action of its flexible compression ring. As the anchor is being tightened, the compression ring will crush if necessary to tightly secure the fixture against the face of the base material.” There is also a plastic star shape below the nut on some bolts and that helps with the loose nut syndrome, something we all try to avoid! Leave them on there, they help. Don’t worry, they aren’t the parts that hold the bolt in the rock.


  • The wedge bolt is secure but the rod sticks up higher than the hanger, is that ok?


It cosmetically looks bad and leaves any wandering climber curious as to how much bolt is left in the rock. If you are absolutely sure you have a sufficient amount of bolt left in the rock, and the wedge and clip are NOT just below the surface, then it is going to hold. If it sticks out too much it could hurt someone or be an unclipping hazard. I recommend loosening the nut, hammering it in again and trying to get it to seat deeper. Just having the tip in the hole isn’t going to satisfy everyone involved!






Chapter 6 - Real Life Shit

This video is of a bolt breaking during a highline whipper. Andy Lewis set up a highline for Alex Mason’s Red Bull eclipse shot and had to use some existing shitty bolts. They were shitty zinc plated bolts that corroded enough to snap during approximately a 5kn whipper which was spread out over that 3 point anchor probably only putting a maximum of 3kn on that bolt.


Zinc Plated Wedge Bolt with Corrosion

Chapter 7 - Buying Guide

As nice as it would be to write in this book, “Just use this 1 bolt”, there is no perfect bolt as each has pros and cons. We want you to know HOW to buy bolts and NOT tell you WHAT to buy. Consider the following when reviewing bolts you see online...

  • Length is TOTAL bolt length for mechanical bolts. If you have a 4 ½” bolt, you may only end up having 3.75” embedded in the rock when you are finished.

  • Some bolts are certified with EN 959:2007 certification or CE/UIAA or some construction certification. And some are not. Go with a reputable company in either case.

  • Don’t buy zinc plated or plated steel or galvanized bolts. If you can’t afford stainless, don’t install bolts. PLX stainless is even better.

  • Read the spec sheets and know what the torque specs are (how tight that bolt is supposed to be wrenched down).

  • Be sure your hanger is made of the same metal as your bolt so you don’t get galvanic corrosion.


These companies sell mechanical bolts that I would take a whipper on.



Bolt Products

BoltProducts is based in Europe and Team-Tough is their distributor in north america. Their products are quality. The only mechanical bolts they sell are wedge bolts.





Fixe Hardware

Fixe Hardware has great selection including Powers sleeve bolts but unfortunately they sell PS (plated steel)... WTF. Their PLX selection is growing too. Manufactured in Spain sells out of US.



Climbtech

ClimbTech sells Powers sleeve, wedge and removable anchors. Unfortunately they also sell PS Powers!?!? US Based.



Vertical Evolution has a single mechanical bolt option that comes in 8mm (too small), 10mm and 12mm… in 316SS or galvanized??? Most of the bolts on their sight are glue in bolts. Based in Italy.





Climbing Technology has great selection of HCR (PLX) and 316L mechanical bolts. Based out of Italy and France.






Raumer sells wedge and double wedge of all sizes. Based in Italy.





Petzl sells quality bolts but they aren’t cheap. Sold everywhere.





Rap Bolting is US distributor to Titan Climbing (they only sell glue ins and are based in the UK) and Rap carries a few mechanical bolts. They carry SS powers but only the short ones. Good for granite, not for softer rock. They also carry some wedge anchors.




DeWalt Power Stud

The Power-Stud was a great 304SS wedge bolt that is about $3 each and is very accessible and comes with ss washer and nut. In our Bolt Buster shear tests, they will snap at 60kn, higher than almost every hanger. Not good for soft rock.


What NOT to Buy


Do Not Use Keith Titanium Bolt

I am NOT convinced Keith Titanium makes bolts that are OK to use but my OCD won’t let me exclude it from this book if I’m attempting to make a complete guide to bolts. I tried buying some but they supposedly don’t sell these in the US and after researching the product this is what I found. Someone couldn’t screw on the nut when they bought it because the threads were poor quality. The website claimed UIAA approved and the UIAA took action and it is no longer on their website. It is not certified to EN959 either. Tested by a third party said this is NOT a titanium alloy like the website states but is commercially pure and not an alloy. The nut and bolt threads appeared cut and not rolled (rolled is stronger and holds up to fatigue). The wedge piece is floppy so a large portion of the bolt gets pulled out of rock when tightening leaving a shallow embedment depth.

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