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The Book of Metal

“Make sure it is hard and that it lasts a long time!”

The Bolting Bible

The Book of Metal

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.

Just like mom always said, “it’s what’s on the inside that counts!” What your bolt is made out of really matters if you want it to last a long time. Most of the bolts you see on the shelf at the local hardware store are not going to make it more than a few seasons. And you can’t just buy whatever you want on any bolt-specific online retailer, even if they market directly to climbers. Some sell zinc plated hardware without being very very clear it should only be used for indoor gyms or very, very, very dry desserts.



Iron ore is mixed with carbon and processed making steel, the most commonly used metal on earth. Fun fact - there are over 3,500 different grades of steel! Most grades of steel will rust quickly if left exposed to air and water. Painting steel, like on cars and bridges, slows the corrosion process down, but paint is not practical in many applications as it doesn’t last very long and will wear off or chip when there is constant metal to metal contact like in climbing.

So the next level of protection is to use chemicals and electricity to apply a very thin metal coating to protect it. Zinc can corrode up to 100x slower than other metals but is much weaker than steel, so steel is often “zinc-plated”. Fun fact - zinc isn’t a hard metal, in fact it is less than half as hard as steel (159DPM hardness vs 70DPM hardness). The zinc is a “sacrificial coating”, so when it is plated on steel, it will always tarnish and corrode first. However it is very thin, and naturally doesn’t give long term protection in any environment with moisture. Once it has fully corroded, the steel underneath begins to rust. Plated steel is generally intended for interior uses.

To make steel last longer, more zinc can be added. However, that takes a completely different process called galvanization. Hot-dipped galvanized coatings is a 7 step process creating a metallurgical bond and can achieve a bond of 3,600 psi (harder than the base steel). This creates the rough surface you see on galvanized nails, but since the threads on galvanized screws can’t be too rough, it is spun in a centrifuge to clear the threads of excess zinc, though it still requires an oversized galvanized nut.

Think of cooking a piece of chicken in a pan with a little oil in the bottom (zinc plating) vs deep frying that turkey (galvanizing). They both have oil on it, but one has a much thicker coating. Zinc plated products are not intended to be an outdoor building material, but galvanized is, however it doesn’t last forever and is not an ideal outdoor anchor. Plated steel bolts can last as little as 3 months in areas like Thailand, Brazil or Hawaii before they can be broken off by hand due to the corrosive nature of water, salt, heat and the chemicals in the rock.


The word “stainless” is thrown around like it is a type of steel, when in fact there are 5 types or categories with a total of 150 grades. Chromium and nickel are the 2 major ingredients to make steel more resistant to corrosion (not corrosion proof). They don’t plate steel with these metals, they melt them together creating an alloy. The two different grades you will see in climbing bolts are 304 and 316 stainless. 304 Stainless Steel is also referred to as 18/8 (18% chromium, 8% nickel). Most stainless climbing bolts and hangers are made out of 304 grade and are significantly more resistant than any plated steel but fail quickly when near the ocean.

316 stainless or “marine-grade” is better because they throw just a little Moly in the recipe. 18% Chromium & 10% Nickel & 2% Molybdenum, and less than 1% of carbon, phosphorus, sulfur, nitrogen. The Molybdenum is added to help resist corrosion to chlorides (salts) like in coastal areas. 316SS is the most corrosion resistant mechanical bolt that you can buy since titanium isn’t available as a mechanical bolt (only as glue ins).

However, in the harsh conditions of Thailand, Brazil and Hawaii, 316 stainless climbing bolts can completely fail within 3 years and so something even more corrosion resistant is required. We played with these discontiued 400 stainless hangers in this EPISODE.

Duplex stainless or PLX stainless or HCR (high corrosion resistant) or 904SS or steel grade 1.4362/1.4462, whatever the hell you want to call it, was offered as a super stainless option. It is roughly 50% ferritic steel and 50% austenitic steel making it twice as strong as either one as ferritic or austenitic by themselves.

Fixe usedto sell their PLX HCR bolts and hangers as a more corrosion resistant version of stainless, however they did have a recall on them because they were rusting, go figure! They narrowed down the batches affected and manufacture the hangers differently now. We currently haven’t found any reports of them failing outside of those batch numbers and we really like how they perform (strength-wise) in BoltBuster tests. Currently FIXE is phasing out their PLX inventory in favor of 316 SS.

However, Peter Randelzhofer put out a paper testing Fixe’s anchor PLX chain links that were in an outdoor covered climbing gym in the Netherlands and they discovered cracks near the welds. Apparently duplex steel 1.4362 is easier to weld but duplex steel 1.4462 is better for corrosion. So the chains they tested were 5kn under the 25kn mbs in only 2 years in mild outdoor conditions.

Petzl sells a HCR wedge bolt with a HCR hanger for the low low price of what a car costs. Bolt Products in Germany have their “Sea Water” series with twisted rod glue ins that supposedly break at 100kn and last 50 years for around €10 each. Here is some toilet reading if you think PLX HCR is interesting. However, titanium shines (metaphorically more than literally) over stainless.

Fun fact: INOX is sometimes stamped into bolts. It is a french way of saying stainless from the word “inoxydable”. It could be 304 or 316 SS but it doesn’t mean duplex stainless, that has PLX stamped into it.


With a tensile strength similar to alloy steel, almost half the density of steel (56%) and platinum level of corrosion resistance, it is the “Cadillac” of all bolts. It is estimated that they can last up to 200 years (see

Fun fact: titanium is the 9th most abundant element on earth and melts at 3,135F (400F more than steel). Titan Climbing manufactured the first certified titanium glue in bolt. It’s a “P” shape made from one continuous rod so there is no structural weld point to break. It requires a 14mm, or ⅝ inch hole and has an MBS of 35kn.