I'm in the market for some 8mm throughbolts. Whilst I could find some discussion of the pros and cons of throughbolts as opposed to spits/resins etc, I couldn't find much about what is expected of the throughbolt itself.

So what sort of specs should I be looking for? I get that this depends on their use case, but how should I be choosing?

For example I might use an A4 stainless bolt if I wanted a longer life, or to avoid any staining of the rock. But what sort of permissable tension/shear loads should I be looking for? Should I be looking for ICC (US) approval? How about Seismic C1 and C2 ratings?

I know that the Dachstein expedition has used Fischer FBZ II 8/10 in the past (a mixture of the stainless R variant and the non-stainless variant), but they're not easily sourced in the UK, instead they're pushing the higher spec, and higher cost, FAZs.

What is everybody else using?

The Raumer studs are not unreasonably priced, are 316/A4, and are double cone in 8 or 10mm. The shortest I would use for rigging is the 78mm 8mm one. I?m sure your friendly caving retailer would be happy with a bulk purchase as they are in stock.

They have at least made an effort to design and test something for climbing and caving for placement in rock rather than concrete, and they are heavily used for real, including being fallen on a lot by climbers (usually the 10mm).

Personally I would overdrill so they can be knocked in flush, and use thread lock for long term use with a hanger left on it (although the Raumer one has a sort of locking nut on it now).

I used to use Hilti A2, and I saw some a couple of years ago I placed nearly 30 years ago that looked like new. I am deeply unworried about the safety of these things in sound rock.

For exploratory rigging I basically buy the cheapest i can on eBay.    Typically i'll buy 65mm long, or 50mm if it's specifically for a long bolt climb. If i'm getting stainless for what may become a tourist route (but yet doesn't warrant a P-Bolt quite yet) i'll get 75mm or maybe longer.

Only features i really look for (as long as not much more cost) is a top section that is not threaded. This means that the thread doesn't become broken during hammering, allowing for the hanger to be easily removed upon derigging without risking the whole bolt turning in the hole.

Also i'll try get fully threaded. This is handy if your drill battery runs out halfway down the hole but it's just about deep enough to get something in. 

Both these features shown in this example:

I cut open my cordura suit and my shoulder prussicking up a tight pitch in JH that had rusty old throughbolts protruding out of the wall from the original bolt climb. Luckily I had a lump hammer on me and was able to take out my rage on the offending items, but I was bleeding for a while, a good way from home. Surely for exploratory rigging it would be better to use good-quality removeable screws and only use (stainless) throughbolts for the final anchors? Then at least it's left nice and neat for future use?

Screwfix are my go-to for through bolts. I guess it varies slightly depending on where you are but they're usually around 20-40p per bolt for the cheapest ones. 75mm seems to be a pretty standard length. I'd agree with all of what Rob says regarding thread in best case scenario though. Also as he says depends what you want to use them for as to how fussy you get. Chunky stainless ones from inglesport are nearly 10x the cost but feel much safer to hang off especially if there will be a lot of traffic.

nobrotson said:

Screwfix are my go-to for through bolts. I guess it varies slightly depending on where you are but they're usually around 20-40p per bolt for the cheapest ones. 75mm seems to be a pretty standard length. I'd agree with all of what Rob says regarding thread in best case scenario though. Also as he says depends what you want to use them for as to how fussy you get. Chunky stainless ones from inglesport are nearly 10x the cost but feel much safer to hang off especially if there will be a lot of traffic.

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Urgh, not Screwfix on principle At least with Fischer they might be crap, but they'll be _reliably_ crap

I think I bought a shedload of bolts from this place:
https://www.fastco.co.uk/fischer-fxa-m8-x-71mm-zinc-plated-through-bolt-article-523131-pack-of-50.html

In fact, I still have shedloads (non-stainless) so you could probably just ask me I've also still got some of the ?2 a shot Raumer double expansion cone 316L stainless, in both 8mm and 10mm... optimism for buying bolts exceeded the opportunities to place them! (purely in Austria)

I?m curious to know what you are going to do (do already) with a line of carbon steel stud bolts if you don?t over drill the holes. Knock them off with a lump hammer after? You surely can?t leave them sticking out?

There are lots of things you can just put in a blank 8mm hole these days. Screws, or the Petzl things if you are posh.

pwhole said:

Surely for exploratory rigging it would be better to use good-quality removeable screws and only use (stainless) throughbolts for the final anchors? Then at least it's left nice and neat for future use?

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Couldn't agree more (other than using resin anchors for the "final" anchors in the UK). Pretty hard to justify other options in my opinion.

I would not use a bolt without a European Technical Approval (ETA) or equivalent and therefore choose something like Fischer, Heco, Hilit, Petzl or Raumer. The price difference to no-name or own brand is negligible, and when I'm hanging off it I'd rather not wonder about steel quality and manufacturing tolerances.*

Personally I use Fischer FXA through bolts (8/10x71, Art. No. 523131) for bolt climbing, I also have a box of 8/30x91 (Art No. 523132) if I suspect there to be a layer of crap on top that I can't spend hours hammering away or the rock is of a generally more fragile nature. Holes are always over-drilled so I can hammer the bugger back after.
The two lengths are not based on any safety research I am aware of but purely battery life considerations and what I'm comfortable with.

I've only used self-taping concrete screws for downwards bolting in quarries (rather than caves) because opportunities to do so aren't exactly plenty full in the UK. They are certainly preferable from a conservation viewpoint; unfortunately I've found stainless steel ones to be a) difficult to come by and b) very expensive. Simon Wilson and Rolf Siegenthaler make good points for using them in their articles.
My attempts to use them for bolt climbing (Heco MMS-plus 7.5x60) have not been overly successful, even with a ratchet spanner I find it too difficult to get the screw to bite with a fully stretched out arm.
Especially for exploratory bolting I'd 100% go with self-taping concrete screws, if it ends up going somewhere the 8mm holes can easily be reused or enlarged for expansion or other anchors. This also avoids issues with badly bolted pitch heads being "ruined" by fracturing the rock with expansion bolts.


*Anecdotally, I have measured differences in OD of 0.5mm in Excalibur screwbolts. I'm no engineer, but that's way more than I'm comfortable with.

Has anyone used these underground much? Not cheap, but I would think 2-3 of them would be very handy. Can they be reused indefinitely? 50mm depth.

I?ve got 3 of the Petzl removable anchors and they are excellent for exploratory trips.

I lent them to a friend of mine a couple of weeks ago for a clandestine exploratory trip in a Derbyshire cave and they proved very effective. If it went, which it did in their case, the hole can be easily drilled out to accommodate a resin type anchor.

As to them being used indefinitely, only time will tell.

Mark

Thank you, very helpful discussion!

I'm not anti concrete screws by any means, but I don't see the division of "exploratory" vs "trade-route" as being black and white, so I think there is a middle ground use case for throughbolts between screws and resin anchors. The Dachstein is a great example - you might spend a decade exploring something only to decide it doesn't go. So whilst you could do your initial push on screws you'd want to drill them out and replace them with something sturdier before too long, and that sturdier thing could be a stainless throughbolt.

Very helpful tips re. threading; I've definitely fallen foul of throughbolts with threaded top sections that break then weld during tapping in.

I'm not much of a fan of throughbolts myself but that is a different topic.  I did notice a comment in the Mulu Caves Project equipment report earlier this year.  It stated quite firmly

Please only buy rated throughbolts from Hilti or Fischer in future

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The guy who wrote it is a very experienced technical caver and a big fan of throughbolts.

Badlad said:

I'm not much of a fan of throughbolts myself but that is a different topic.  I did notice a comment in the Mulu Caves Project equipment report earlier this year.  It stated quite firmly

Please only buy rated throughbolts from Hilti or Fischer in future

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The guy who wrote it is a very experienced technical caver and a big fan of throughbolts.

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'rated' is an interesting thing... All the cheap 8mm throughbolts described so far are, as far as I know, rated for hanging things off non-cracked concrete and are not rated as caving/climbing/rope access anchors, so what does 'rated' mean here? Just has an ETA for something, regardless of what it is?

I thought the 8mm Raumers didn't either, but turns out (in combination with the Raumer ring hanger or caving maillon hanger) do pass EN959:2018 (not rated for EN959:2007; don't know if that's due to a change in standards or they just didn't certify them).

I suspect 'rated' mostly means from a known trusted supplier.  I think the issue with the Mulu equipment's stock was that some of the throughbolts were unidentifiable and of inferior quality. I'm guessing as I wasn't there for the audit but did note the comments in the report relevant to this discussion.  When you are hanging your life on an industrial fixing you do need to have some confidence in it. This is presumably one way of achieving that.

aricooperdavis said:

I'm not anti concrete screws by any means, but I don't see the division of "exploratory" vs "trade-route" as being black and white, so I think there is a middle ground use case for throughbolts between screws and resin anchors. The Dachstein is a great example - you might spend a decade exploring something only to decide it doesn't go. So whilst you could do your initial push on screws you'd want to drill them out and replace them with something sturdier before too long, and that sturdier thing could be a stainless throughbolt.

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Fair comment. I guess I'm not a fan of throughbolts in general but as Badlad said, that's probably a different topic.

Having had issues with non-stainless throughbolts (Fischer Faz II, apparently) adhering to the nuts between trips in subsequent years, I would probably only want to use stainless ones for anything needing to last longer than concrete screws.

MarkS said:

Having had issues with non-stainless throughbolts (Fischer Faz II, apparently) adhering to the nuts between trips in subsequent years, I would probably only want to use stainless ones for anything needing to last longer than concrete screws.

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I guess climate is an issue as well. Deep in the Dachstein, all the bolts might be damp but they are almost in a deep-freeze at a steady 2 degrees, so even decades-old bolts are not necessarily that rusty (although I'd still rather use stainless!). Whereas in the jungle, I can imagine them rusting by the end of the exped...

andrewmc said:

I guess climate is an issue as well. Deep in the Dachstein, all the bolts might be damp but they are almost in a deep-freeze at a steady 2 degrees, so even decades-old bolts are not necessarily that rusty (although I'd still rather use stainless!). Whereas in the jungle, I can imagine them rusting by the end of the exped...

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I suspect you're right, but I was referring to anchors placed in cold alpine caves in Montenegro!

Interesting discussion. The rating element is a poignant topic, and i think i currently sit far on one side of the scale. At risk of being eaten alive, here's my viewpoint.

An M8 bolt is a very strong item for the application we use it in, especially when generally used in shear. I don't know figures to back this up, but i'd guess a safety factor of 10 even at a low steel class, and also allowing for a reasonable dynamic loading. The axial strength of the bolt should also be exceptionally high, as a typical tightening force in normal (non-caving) operation would be far greater than that of human loading.

I can understand a risk associates with the collar which could be deemed as a mechanical part so more susceptible to material quality or design. However it is designed to fail, i.e. the collar breaks, deforms, and moulds into the cone below, so i'm not sure really how that could go wrong (in a dangerous way).

Further more, we never (if possible!) hang off one bolt, with Y-hangs to not only spread the load but also there in case of item failure. So there is safety built into the way we rig.

Yes academically unrated bolts aren't designed to hang heavy things off in a safety critical way. But neither are the handholds we rely on for every single trip, nor the robustness of the roof when moving through chokes. Caving is dangerous, especially at the pointy end, in magnitudes far far greater than using unrated M8 bolts, which incidentally i've never seen fail due to poor product quality.

However, if there was an M5 through bolt discussion....

I have always used Raumer SS M8 and M10 bolts - always liked the twin collars on the long ones. These have always been used in mines with solid limestone and sandstone.